Image forming apparatus and calibration reference chart

ABSTRACT

Based on a read value of a calibration reference chart including achromatic patches and chromatic patches having different concentrations and a reference value of the calibration reference chart, a masking coefficient according to each hue area is calculated. A gradation conversion is performed on an image signal output from an image reading unit. The image signal is corrected based on the masking coefficient. Consequently, it is possible to reduce a difference in performance of a scanner between units.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present document incorporates by reference the entire contents ofJapanese priority documents, 2005-017524 filed in Japan on Jan. 25,2005, 2005-267320 filed in Japan on Sep. 14, 2005, 2005-012100 filed inJapan on Jan. 19, 2005 and 2005-017525 filed in Japan on Jan. 25, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus that has afunction of outputting data to an external device.

2. Description of the Related Art

Conventionally, due to fluctuation in spectral sensitivities of a chargecoupled device (CCD) or an infrared-ray cut filter, and deteriorationwith time and use of an optical system, a read value of a scanner inreading image data varies depending on a unit. Even when the identicalcolor document is read, each of the units outputs a different imagesignal. As a result, an image output to be displayed or printed by eachof the units appears in different colors.

In a conventional technology for adjusting the difference in color, animage forming apparatus performs a hue-division-masking color-correctionprocessing. The image forming apparatus includes a unit that calculatesa masking coefficient based on a value of an input image signal obtainedby reading an original document of which a spectral characteristiccorresponding to a point where hue is divided is known, and C, M, Y, andK recording values of a developing unit optimal for the reproduction ofthe color of the original document. Moreover, an image forming apparatusmay include a unit that calculates a masking coefficient by a differencevalue between an output image signal obtained by converting the inputimage signal obtained by reading an original document, a spectralcharacteristic of which is known by a predetermined masking coefficient,and an output value obtained by converting, with the predeterminedmasking coefficient, an input image signal obtained when the original isread by a reading apparatus having a standard spectral characteristic.Such technologies are disclosed in, for example, Japanese PatentApplication Laid-Open No. 2002-290761.

In an image processing method according to another conventionaltechnology, a reference chart having color images of different gradationlevels is read by a reading unit to create the correction data of thereading unit based on the image data of the read reference chart andreference data stored in advance in association with the color images ofthe different gradation levels. The image output by the output unitbased on the reference data for the correction of the output unit isread by the reading unit corrected by the created correction data. Basedon the read image data, correction data of the output unit is created.Such a technology is disclosed in, for example, Japanese Patent No.2643951.

In still another conventional technology, an image processing apparatuscorrects a color represented by a color image signal to be a colorsuitable for an output apparatus from which the color image signalshould be output. This image processing apparatus includes a hue-areajudging unit that determines a hue area that includes, among plural hueareas formed to include a plane in a color space parallel to abrightness axis as a boundary, a signal color represented by the colorimage signal and a correction unit that corrects a signal coloraccording to the hue area. Such a technology is disclosed in, forexample, Japanese Patent Application Laid-Open No. 2004-13361.

With the recent development of communication technologies, a situationsurrounding color copying apparatuses has significantly changed. Alarge-scale image formation system in which more than one color copyingapparatus is connected via the Internet or the like to provide thetransmission and reception of data among plural color copyingapparatuses has been widely used.

In the large-scale image formation system, image data read by a scannerin a color copying apparatus is sent to another color copying apparatusand an image processing unit (IPU) or a printing unit in the colorcopying apparatus that has received the image data can perform imageprocessing for printing.

For example, when an original document is desired to be copied in alarge quantity in a short period of time, the original document is readby a scanner in one color copying apparatus, and the read image data issent to plural other color copying apparatuses. Thus, the read imagedata can be printed out by plural units of color copying apparatusessimultaneously.

In another example, when original documents existing at more than onelocation are desired to be collectively copied at one location, theoriginal documents are read by a scanner in a color copying apparatus ineach location and the read image data are sent to one color copyingapparatus. Thus, the original documents in different places can beprinted by one color copying apparatus.

However, in the conventional technologies, when plural color copyingapparatuses are connected to provide data transmission and reception anda color copying apparatus different from a color copying apparatus thathas read the original document performs printing, a colorreproducibility is low compared to when a single color copying apparatusperforms printing because a read value of a scanner in reading imagedata varies depending on a unit even when the identical color documentis read.

An image processing parameter used for image processing by a colorcopying apparatus is obtained by calibrating a scanner and a printingunit in the color copying apparatus in pairs. Thus, all color copyingapparatuses do not always store therein the same image processingparameter. However, in the conventional technology, a color copyingapparatus different from a color copying apparatus that has read theoriginal document performs image processing to print an image. Thus, acombination of the scanner that has read the original document and theprinting unit that has performed the printing is different from acombination that was calibrated. Consequently, when image processingparameter of the color copying apparatus that has read the originaldocument and the image processing parameter of the color copyingapparatus that has received the image data are different, the colorreproducibility is low compared to when a single color copying apparatusperforms printing.

The problems described above are more conspicuous, when one originaldocument is read by one color copying apparatus, and read image data ofthe original document is printed by plural color copying apparatuses.Copies having unequal color reproducibility are printed in a largequantity.

Similarly, the problems are conspicuous when original documents locatedat more than one location are collectively printed at one location byone color copying apparatus.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least solve the problemsin the conventional technology.

An image forming apparatus according to one aspect of the presentinvention includes a color correcting unit that includes a scanning unitconfigured to optically scan an original document to read an image, andto output an image signal; a first converting unit configured to performa gradation conversion on the image signal; a hue-area detecting unitconfigured to detect, among a plurality of hue areas having a planeprovided in parallel with a brightness axis in a color space as aboundary, a hue area including a signal color represented by a colorimage signal; and a correction unit configured to correct the signalcolor according to the hue area; a reference-data storing unitconfigured to store reference data corresponding to a patch in areference chart including a plurality of achromatic patches havingdifferent gradation levels and a plurality of different chromaticpatches, the reference chart obtained by reading an image by thescanning unit; and a parameter generating unit configured to generate,based on the reference data, a hue division parameter to be set in thehue-area detecting unit and a color correction parameter to be set inthe correction unit.

An image forming apparatus according to another aspect of the presentinvention includes means for optically scanning an original document toread an image, and to output an image signal; means for performing agradation conversion on the image signal; means for detecting, among aplurality of hue areas having a plane provided in parallel with abrightness axis in a color space as a boundary, a hue area including asignal color represented by a color image signal; means for correctingthe signal color according to the hue area; means for storing referencedata corresponding to a patch in a reference chart including a pluralityof achromatic patches having different gradation levels and a pluralityof different chromatic patches, the reference chart obtained by readingan image by means for scanning; and means for generating, based on thereference data, a hue division parameter to be set in means fordetecting the hue-area and a color correction parameter to be set inmeans for correcting the signal color.

An image forming apparatus according to still another aspect of thepresent invention has a function of outputting an image read by theimage forming apparatus from another image forming apparatus. The imageforming apparatus includes a reading unit configured to read an image,and to output an image signal; a converting unit configured to performgradation conversion on the image signal; a chart reading unitconfigured read a calibration reference chart that includes a pluralityof chromatic patches having different hue areas that have a planeprovided in parallel with a brightness axis in a color space as aboundary, and a plurality of achromatic patches having differentconcentrations; a reference-value storing unit configured store areference value corresponding to each of the chromatic patches; a firstcorrecting unit configured to correct R, G, and B signals correspondingto each of the hue areas based on the reference value and a read valueof the chromatic patches obtained by reading the calibration referencechart; a masking-coefficient calculating unit configured to calculate amasking coefficient corresponding to each of the hue areas fromcorrected R, G, and B signals and C, M, Y, and K signals correspondingto each of the hue areas; and a second correcting unit configured tocorrect the image signal on which the gradation conversion has beenperformed, based on the masking coefficient.

An image forming apparatus according to still another aspect of thepresent invention has a function of outputting an image read by theimage forming apparatus from another image forming apparatus. The imageforming apparatus includes means for reading an image to output an imagesignal; means for performing gradation conversion on the image signal;means for reading a calibration reference chart that includes aplurality of chromatic patches having different hue areas that have aplane provided in parallel with a brightness axis in a color space as aboundary, and a plurality of achromatic patches having differentconcentrations; means for storing a reference value corresponding toeach of the chromatic patches; means for correcting R, G, and B signalscorresponding to each of the hue areas based on the reference value anda read value of the chromatic patches obtained by reading thecalibration reference chart; means for calculating a masking coefficientcorresponding to each of the hue areas from corrected R, G, and Bsignals and C, M, Y, and K signals corresponding to each of the hueareas; and means for correcting the image signal on which the gradationconversion has been performed, based on the masking coefficient.

A calibration reference chart according to still another aspect of thepresent invention is a patch type chart used for calibration of an imagereading unit in an image forming apparatus that has a function ofoutputting an image read by the image reading unit from an image outputunit of another image forming apparatus. The calibration reference chartis formed by arranging, on a recording medium, a plurality of chromaticpatches having different hue areas having a plane provided in parallelwith a brightness axis in a color space as a boundary and a plurality ofachromatic patches having different concentrations.

An image forming method according to still another aspect of the presentinvention includes optically scanning an original document to read animage; outputting an image signal; performing a gradation conversion onthe image signal; detecting, among a plurality of hue areas having aplane provided in parallel to a brightness axis in a color space as aboundary, a hue area including a signal color represented by a colorimage signal; and correcting the signal color according to the hue area;storing reference data corresponding to a patch in a reference chartincluding a plurality of achromatic patches having different gradationlevels and a plurality of different chromatic patches, the referencechart obtained by reading an image; and generating, based on thereference data, a hue division parameter to be set at detecting thehue-area and a color correction parameter to be set at correcting thesignal color.

An image forming method according to still another aspect of the presentinvention is for forming an image in an image forming apparatus that hasa function of outputting an image read by the image forming apparatusfrom another image forming apparatus. The method includes reading animage; outputting an image signal; reading a calibration reference chartthat includes a plurality of chromatic patches having different hueareas that have a plane provided in parallel with a brightness axis in acolor space as a boundary, and a plurality of achromatic patches havingdifferent concentrations; storing a reference value corresponding toeach of the chromatic patches; correcting R, G, and B signalscorresponding to each of the hue areas based on the reference value anda read value of the chromatic patches obtained by reading thecalibration reference chart; calculating a masking coefficientcorresponding to each of the hue areas from corrected R, G, and Bsignals and C, M, Y, and K signals corresponding to each of the hueareas; and correcting an image signal obtained by performing gradationconversion on output image signal, based on the masking coefficient.

The other objects, features, and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed description of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a system configuration in which color copyingapparatuses using an image forming apparatus according to a firstembodiment of the present invention are linked;

FIG. 2 is a schematic of an electrophotographic color copying apparatus;

FIG. 3 is an enlarged view of a scanner section and an ADF section inthe color copying apparatus shown in FIG. 2;

FIG. 4 is a top view of the color copying apparatus shown in FIG. 2;

FIG. 5 is a schematic of a control system of the color copying apparatusshown in FIG. 2;

FIG. 6 is a schematic of an IPU and a printer section of the colorcopying apparatus shown in FIG. 2;

FIG. 7 is a block diagram of an MTF shown in FIG. 6;

FIG. 8 is a schematic of a Laplacian filter shown in FIG. 7;

FIG. 9A is a schematic of a sub-scanning-direction edge-detectionfilter;

FIG. 9B is a schematic of a main-scanning-direction edge-detectionfilter;

FIG. 9C is a schematic of an oblique-direction detection filter;

FIG. 9D is a schematic of another oblique-direction detection filter;

FIG. 10 is a schematic for illustrating table conversion of an edgelevel by a table conversion circuit;

FIG. 11 is a schematic of a color space for explaining a colorcorrection processing;

FIG. 12 is a schematic of a color space for explaining a colorcorrection processing;

FIG. 13 is a schematic of a color space for explaining a colorcorrection processing;

FIG. 14 is a schematic of a color space for explaining a colorcorrection processing;

FIG. 15 is a flowchart of a hue determination processing;

FIG. 16 is a schematic of a color plane for explaining color correctionprocessing;

FIG. 17A is a schematic for illustrating pixel numbers when totalthirty-six pixels, which is 6 pixels in a main scanning direction×6pixels in a sub-scanning direction, are used in a dither processing;

FIG. 17B is a schematic for illustrating an index table when totalthirty-six pixels, which is 6 pixels in a main scanning direction×6pixels in a sub-scanning direction, are used in the dither processing;

FIG. 18A is a schematic of a gradation processing table for 2 pixels inthe main scanning×2 pixels in the sub-scanning in the case of an indextable in FIG. 17B;

FIG. 18B is a schematic of a gradation processing table for 2 pixels inthe main scanning×2 pixels in the sub-scanning in the case of an indextable in FIG. 17B;

FIG. 18C is a schematic of a gradation processing table for 2 pixels inthe main scanning×2 pixels in the sub-scanning in the case of an indextable in FIG. 17B;

FIG. 19A is a schematic for illustrating pixel numbers when the pixelnumbers shown in FIG. 17A are shifted by one pixel in the main scanningdirection;

FIG. 19B is a schematic for illustrating an index table when the pixelnumbers shown in FIG. 17A are shifted by one pixel in the main scanningdirection;

FIG. 20 is a schematic for illustrating an index table corresponding todither of 2 pixels in the main scanning direction×2 pixels in thesub-scanning direction;

FIG. 21 is a schematic for illustrating an area processing by an areaprocessing section shown in FIG. 6;

FIG. 22 is a block diagram of a laser modulation circuit of a printersection in the color copying apparatus shown in FIG. 2;

FIG. 23 is a block diagram of the scanner section shown in FIG. 2;

FIG. 24 is a schematic for illustrating white correction and blackcorrection by a shading correction circuit shown in FIG. 23;

FIG. 25 is a schematic for illustrating a sample hold processing for areading signal by an S/H circuit shown in FIG. 6;

FIG. 26 is a schematic of a linkage color-correction chart used inscanner calibration;

FIG. 27 is a sequence diagram of a scanner calibration by the colorcopying apparatus shown in FIG. 2;

FIG. 28 is a schematic of a display showing a various-adjustmentsscreen;

FIG. 29 is a schematic of a display showing a scanner-calibration startscreen;

FIG. 30 is a schematic of a display showing a screen that indicates thata linkage color-correction chart is being read in a scanner calibrationmode;

FIG. 31 is a schematic of a quaternary chart in the scanner calibration;

FIG. 32 is a flowchart of a scanner calibration processing;

FIG. 33 is a schematic of a display showing a scanner calibrationscreen;

FIG. 34 is a schematic of a display showing a screen for a factoryadjustment value;

FIG. 35 is a schematic of a display showing a screen for a read value;

FIG. 36 is a schematic of a display showing a screen for a correctioncoefficient;

FIG. 37 is a flowchart of the scanner calibration processing;

FIG. 38 is a schematic of classes of scanner calibration;

FIG. 39 is a table of reading reference values of chromatic andachromatic patches for yellow toner correction;

FIG. 40 is a schematic for illustrating a relation between CCD spectralsensitivity of a blue signal and a spectral reflection factor of ayellow toner;

FIG. 41 is a schematic for illustrating a relation among a spectralreflection factor characteristic of cyan ink, a spectral reflectionfactor of area rate 50% yellow toner, and a read value of the bluesignal;

FIG. 42 is a quaternary chart of an automatic color correction (ACC)pattern read value correction table;

FIG. 43 is a table of reading reference values of chromatic andachromatic patches for the correction of cyan toner;

FIG. 44 is a schematic of a display showing an automaticgradation-adjustment screen;

FIG. 45 is a schematic of a display showing anautomatic-gradation-correction start screen;

FIG. 46 is a flowchart of an ACC processing by the color copyingapparatus shown in FIG. 2;

FIG. 47 is a schematic of a gradation pattern output on transfer paperin the ACC processing;

FIG. 48 is a schematic of a display showing a screen requesting a userto set the transfer paper on which a gradation pattern is output;

FIG. 49 is a schematic of a display showing a screen indicating that areading of the set transfer paper is in process;

FIG. 50 is a quaternary chart for illustrating a calculation method inthe ACC processing;

FIG. 51 is a schematic for illustrating creation of a green conversiontable;

FIG. 52 is a flowchart of a gradation-conversion-table creationprocessing in the ACC;

FIG. 53 is a flowchart of a development-characteristic detectionprocessing;

FIG. 54 is a schematic of a detection pattern formed on a photosensitiveelement drum by development characteristic detection processing and adetection status by an optical sensor;

FIG. 55 is a schematic for illustrating a correction processing for animage signal in the ACC processing;

FIG. 56 is a circuit block diagram of an IPU and a printer section of acolor copying apparatus according to a second embodiment of the presentinvention;

FIG. 57 is a flowchart of a correction by scanner data calibration; and

FIG. 58 is a schematic for illustrating an area processing by an imageseparation circuit shown in FIG. 56.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are explained below indetail with reference to the accompanying drawings.

Note that, although examples described below are preferred examples ofthe present invention and thus have various technically preferablelimitations, the scope of the present invention is not limited to theseexamples unless the following description includes a particulardescription for limiting the present invention.

In a first embodiment of the present invention, the present invention isapplied to, as an example of an image forming apparatus, anelectrophotographic color copying apparatus 1, a so-called multifunction peripheral (MPF), that includes a copy function, a facsimile(FAX) function, a printing function, a scanner function, and a functionto deliver an input image (an original image read by the scannerfunction or an image input by the printer or the FAX function).

FIG. 1 is a schematic of a system configuration in which the colorcopying apparatuses 1, to which the image forming apparatus of thepresent invention is applied, are linked and connected. As shown in FIG.1, each of the respective color copying apparatuses 1 is connected via alocal area network (LAN) cable 1000 to be capable of transmitting andreceiving data. Such a color copying apparatus 1 functions as a childcolor copying apparatus when the color copying apparatus 1 is linked andconnected to another color copying apparatus 1. Specifically, to copyonly one original in a large quantity and in a short period of time, theoriginal is read by a scanner section 300 of one color copying apparatus1 and read original image data is sent to the other linked color copyingapparatus 1. The respective color copying apparatuses 1 perform imageprocessing to print and output images via printer sections 100simultaneously. This is a linkage output function.

In such a case, due to fluctuation in spectral sensitivities of CCDs ofthe scanner sections of the respective color copying apparatuses 1,fluctuation in spectral sensitivities of infrared-ray cut filters forremoving infrared ray components, deterioration with time and use of ascanner optical system, and the like, machines may have different readvalues of original image data. Thus, even when the same color originalis read by the machines, the scanner sections 300 of the respectivecolor copying apparatuses 1 output different image signals. This causesa difference between the output colors for display and printed colors.In order to solve the problem, the present invention makes it possibleto set an image processing parameter for the purpose of reducing thedifferences in the scanner sections 300 of the respective color copyingapparatuses 1, improving printer adjustment accuracy, and reducingfluctuation in adjustment. Details are described below.

FIG. 2 is a schematic of the electrophotographic color copying apparatus1. In FIG. 2, in the color copying apparatus 1, the printer section 100serving as image formation unit, a sheet feeding section 200, thescanner section 300 serving as an image reading unit, and the like arebuilt in a body housing 2. A contact glass 3 is disposed on an uppersurface of the body housing 2. An upper part of the color copyingapparatus 1 has an auto document feeder (ADF) 400. The ADF 400 separatesa plurality of originals G set on an original stand 40 one by one toconvey the originals with a roller and an original conveyor belt 402 toan original reading position, where the originals are read by thescanner section 300, on the contact glass 3. The read originals G aredischarged onto a sheet discharge tray (not shown) by the originalconveyor belt 402.

The sheet feeding section 200 includes a sheet feeding tray 201, areversing section 202, a conveyance roller (not shown), and the like andseparates a plurality of pieces of transfer paper (transfer materials) Pon the sheet feeding tray 201 one by one to convey the transfer paper tothe printer section 100. The reversing section 202 reverses front andback surfaces of the transfer paper P subjected to image formation bythe printer section 100 to send the transfer paper P to the printersection 100 again to subject the back surface to image formation. Oneside surface of the body housing 101 includes a sheet feeding tray 203on which the transfer paper P is set manually. The sheet feeding section200 also conveys the transfer paper P on this sheet feeding tray 203 tothe printer section 100.

A side surface of the body housing 101 on the opposite side of the sheetfeeding tray 203 has a sheet discharge tray 204 for sequentiallydischarging the transfer paper P subjected to image formation by theprinter section 100 to the sheet discharge tray 204.

The printer section 100 is provided in substantially the center of thebody housing 2. An annular intermediate transfer belt 101 is provided insubstantially the center of the printer section 100 over a predeterminedlength in an oblique direction along a longitudinal direction of theprinter section 100. The intermediate transfer belt 101 is disposed tosurround a driving roller 102 and a transfer roller 103 and is rotatedand driven in a clockwise direction indicated by an arrow in FIG. 2.Along this intermediate transfer belt 101, organic photosensitiveelement (OPC) drums 104K to 104C having a diameter of φ30 millimetersserving as four image bearing members of black (K) and three colors ofyellow (Y), magenta (M), and cyan (C) are disposed. Around thephotosensitive element drums 104K to 104C, electrification chargers 105Kto 105C for electrification of surfaces of the photosensitive elementdrums 104K to 104C, a laser optical system 106 that emits a laser beamto the surfaces of the uniformly electrified photosensitive elementdrums 104K to 104C to form an electrostatic latent image, a blackdevelopment unit 107K and three color development units 107Y, 107M, and107C of Y (yellow), M (magenta), and C (cyan) that supply respectivecolor toners to electrostatic latent images to develop the images toform toner images of the respective colors, bias rollers 108K to 108Cthat apply a transfer voltage to the intermediate transfer belt 101, acleaning device (that is not denoted by a reference numeral) thatremoves the toner remaining on the surfaces of the transferredphotosensitive element drums 104K to 104C, a charge removing sectionthat removes changes remaining on the surfaces of the transferredphotosensitive element drums 104K to 104C, and the like are disposed.

The printer section 100 uniformly charges the photosensitive elementdrums 104K to 104C rotated in a counter-clockwise direction with theelectrification chargers 105K to 105C, irradiates laser beams modulatedby color data of the respective colors on the uniformly chargedphotosensitive element drums 104K to 104C from the laser optical system106 to form electrostatic latent images. The printer section 100supplies toners of the respective colors to the respectivephotosensitive element drums 104K to 104C on which the electrostaticlatent images are formed from the development units 107K to 107C of therespective colors to form toner images. The printer section 100 uses thebias rollers 108K to 108C to apply a transfer voltage to theintermediate transfer belt 101 and sequentially transfers the respectivetoner images onto the photosensitive element drums 104K to 104C to besuperposed one on top of another on the intermediate transfer belt 101to transfer a full color toner image.

In the printer section 100, a pressure roller 109 is arranged in aposition opposed to the transfer roller 103 across the intermediatetransfer belt 101. The transfer paper P is transferred to a spacebetween the pressure roller 109 and the transfer roller 103 from thesheet feeding section 200. On a conveyance path of the transfer paper Pto the pressure roller 109 and the transfer roller 103, a conveyanceroller 110 and a resist roller 111 are provided. The conveyance roller110 conveys the transfer paper P from the sheet feeding section 200 tothe resist roller 111 and the resist roller 111 adjusts timing for theconveyed transfer paper P and the toner image on the intermediatetransfer belt 101 to convey the transfer paper P to the space betweenthe pressure roller 109 and the transfer roller 103.

The transfer roller 103 applies a transfer voltage to the intermediatetransfer belt 101 to transfer the toner image onto the intermediatetransfer belt 101 to the transfer paper P conveyed to the space betweenthe transfer roller 103 and the pressure roller 109.

In the printer section 100, on a downstream side of the conveyancedirection of the transfer paper P onto which the toner image is alreadytransferred, a conveyor belt 112 and a fixing unit 113 are provided. Thetransfer paper P onto which the toner image is transferred and which ispeeled from the intermediate transfer belt 101 is conveyed by theconveyor belt 112 to the fixing unit 113. The fixing unit 113 includes afixing roller 114 heated to a fixing temperature and a pressure roller115 brought into press contact with the fixing roller 114. The fixingunit 113 conveys the conveyed transfer paper P while heating andpressurizing the transfer paper P with the fixing roller 114 and thepressure roller 115, which are driven to rotate, fixes the toner imageon the transfer paper P, and discharges the transfer paper P onto asheet discharge tray 204 provided on a side surface of the body housing2.

As shown in FIG. 3 in an enlarged form, the scanner section 300 includesa first carrier 305 including a halogen lamp 302 having a lampshade 301and a first mirror 303 for reflecting light from the original G and thehalogen lamp 302 to an original G and a white reference plate (notshown) and a second mirror 304 for reflecting reflected light from theoriginal G and the white reference plate, a second carrier 308 includinga third mirror 306 and a fourth mirror 307 for sequentially reflectinglight reflected by the second mirror 304, two switchable infrared-raycut filters 309 and 310, a lens 311, a CCD 312 serving as aphotoelectric conversion element, and the like. While moving the firstcarrier 305 and the second carrier 308 at a predetermined movement speedin a sub-scanning direction (a direction indicated by an arrow “a” shownin FIG. 3), the scanner unit 300 irradiates reading light on theoriginal G on the contact glass 3 from the halogen lamp 302 on the firstcarrier 305 and reflects reflected light from the original G to thethird mirror 306 on the second carrier 308 with the second mirror 304.The scanner section 300 uses the third mirror 306 to reflect thereflected light from the second mirror 304 in a direction of the fourthmirror 307 and uses the fourth mirror 307 to reflect the reflected lightin a direction of the infrared-ray cut filters 309 and 310. Theinfrared-ray cut filter 309 or the infrared-ray cut filter 310positioned on the optical path at the point are used to cut infrared rayto cause the light to be incident on the lens 311. The scanner section300 collects the incident light to the CCD 312. The CCD 312 subjects theincident light to photoelectric conversion to read the image of theoriginal G and output the image as an analog image signal.

In the color copying apparatus 1, the upper surface part of the bodyhousing 2 includes, as shown in FIG. 4, an operation section 500. Theoperation section 500 includes a start key 501, a clear/stop key 502, anumeric keypad 503, an interruption key 504, a memory call key 505, apreheating/mode clear key 506, a color adjustment/registration key 507,a program key 508, an option key 509, an area processing key 510, aliquid crystal screen 511, and the like.

A control system of the color copying apparatus 1 is constituted asshown in FIG. 5. The control system includes a central processing unit(CPU) 601 of a system controller 600 that controls the respectivesections of the color copying apparatus 1 to execute the processing bythe color copying apparatus 1, a read only memory (ROM) 602 for storingvarious programs and data, a random access memory (RAM) 603 used as awork memory of the CPU 601, an interface I/O 604 for connecting the CPU601 to various circuit sections, a various sensor control section 605, apower source/bias control section 606, a driving control section 607, anoperation control section 608, a communication control section 609, astorage control section 610, a storage 611, an IPU 612, a laser opticalsystem driving section 613, a toner supply circuit 614, and the like.

Toner concentration sensors 615 provided in the respective Y, M, C, andK development units 107K to 107C, optical sensors 616 a to 616 cprovided in the respective Y, M, C, and K development units 107K to107C, a potential sensor 617, an environment sensor 618, and the likeare connected to the various sensor control section 605. Sensor signalsfrom the respective sensors 615 to 618 are output to the CPU 601 via theinterface I/O 604. This optical sensor 616 a is provided to be opposedto the respective photosensitive element drums 104K to 104C to detect anamount of toner deposited on the photosensitive element drums 104K to104C. The optical sensor 616 b is provided near the respectivephotosensitive element drums 104K to 104C to be opposed to theintermediate transfer belt 101 to detect an amount of toner deposited onthe intermediate transfer belt 101. The optical sensor 616 c is providedto be opposed to the conveyor belt 112 to detect an amount of tonerdeposited on the conveyor belt 112. In a practical use, the amount ofdeposited toner may be detected by any one of the optical sensors 616 ato 616 c.

The optical sensor 616 a is provided at a position outside an image areain an axial direction of the photosensitive element drums 104K to 104Cand near the image area. The optical sensor 616 a includes alight-emitting element (e.g., light-emitting diode) and alight-receiving element (e.g., photo sensor). The optical sensor 616 adetects, for each of the colors, an amount of depositions of toners inthe toner image of the detection pattern latent image formed on thephotosensitive element drums 104K to 104C and an amount of deposition oftoners of the respective colors in the background section. The opticalsensor 616 a also detects a so-called residual potential after chargeremoval for the photosensitive element drums 104K to 104C to output adetection signal to the various sensor control section 605. The varioussensor control section 605 calculates, based on the detection signalfrom the optical sensor 616 a, a ratio of the toner deposition amount inthe toner image of the detected pattern toner image and the tonerdeposition amount in the background section to compare a value of theratio with a reference value to detect fluctuation in imageconcentration. Consequently, the various sensor control section 605performs correction of control values from the respective Y, M, C, and Ktoner concentration sensors 615. Note that the optical sensor 616 a in apractical use is not required to be provided in the respectivephotosensitive element drums 104K to 104C and the toner depositionamount may be detected by any one of the photosensitive element drums104K to 104C.

The toner concentration sensor 615 is provided in the respectivedevelopment units 107K to 107C and detects, based on a change inmagnetic permeability of developers in the development units 107K to107C, toner concentration to output a detection signal to the varioussensor control section 605. The various sensor control section 605compares, based on the detection by the toner concentration sensor 615,the detected toner concentration value with a reference value, and whenit is judged that the toner concentration is lower than a fixed valueand the toner is in shortage, outputs a toner supply signal having amagnitude corresponding to the amount of shortage to the toner supplycircuit 614. Based on the toner supply signal, the toner supply circuit614 supplies toner to the corresponding development units 104K to 104C.

The potential sensor 617 detects the surface potentials of therespective photosensitive element drums 104K to 104C serving as imagebearing members to output a detection signal to the various sensorcontrol section 605.

The power source/bias control section 606 controls power supply to thedevelopment units 107K to 107C and the power supply circuit 619. Thepower supply circuit 619 supplies a predetermined electrificationdischarge voltage to the electrification chargers 105K to 105C, suppliesa development bias of a predetermined voltage to the development units107K to 107C, and supplies a predetermined transfer voltage to the biasrollers 108K to 108C and the electrification chargers 105K to 105C.

The driving control section 607 controls driving of the laser opticalsystem driving section 613 that adjusts the laser output of the laseroptical system 106, the intermediate transfer belt driving section 620that controls the rotation and driving of the intermediate transfer belt101, and the toner supply circuit 614 that supplies toner to thedevelopment units 107K to 107C. The operation control section 608performs, under the control by the CPU 601, acquisition of operationcontents of the operation section 500, lighting control for a lamp orthe like, control for display of a liquid crystal screen, and the like.

The communication control section 609 is connected to a network (e.g.,the Internet, an intranet) to perform communication via the network. Thestorage 611 is constituted by a hard disk or the like and stores, undercontrol by the storage control section 610, various pieces ofinformation (particularly image data).

As shown in FIG. 6, the IPU 612 includes a shading correction circuit701, an area processing section 702, a scanner gamma conversion section703, an image memory 704, an image separation section 705, an interface(I/F) 706, an modulation transfer function (MTF) filter 707, a huedetermination circuit 708, a color conversion under color removal (UCR),a processing circuit 709, a pattern generation section (a gradationpattern generating unit) 710, an enlargement/reduction circuit 711, animage processing circuit 712, an image processing printer gammaconversion circuit (a first image signal converting unit) 713, agradation processing circuit (a color converting unit) 714, a CPU 715, aROM 716, and a RAM 717. The respective sections are connected by a bus718.

The printer section 100 also includes an I/F selector 721, a patterngeneration section (a gradation pattern generating unit) 722, an imageformation printer γ correction circuit (a second image signal convertingunit) 723, and a printer engine 724 for actually performing the imageformation in the printer section 100.

The CPU 715 is connected to the ROM 716 and the RAM 717 via the bus 718and is also connected to the system controller 600 via a serial I/F toreceive a command from the operation section 500 or the like via thesystem controller 600. The CPU 715 determines various parameters for therespective sections of the IPU 612 requiring the parameters based on animage quality mode, concentration information, and area information, orthe like sent from the operation section 500 or the like.

The scanner section 300 subjects the original G on the contact glass 3to color separation of R, G, and B to read the original G with, forexample, 10 bits to output the image signal of the read original G tothe shading correction circuit 701 of the IPU 612.

The shading correction circuit 701 corrects unevenness of an imagesignal input from the scanner section 300 in the main scanning directionto output the image signal as, for example, an 8-bit signal to thescanner gamma conversion section 703.

The area processing section 702 generates an area signal for determiningwhich area in the original G corresponds to currently-processed imagedata. This area signal is used to switch a parameter used in imageprocessing in a subsequent stage. This area processing section 702determines, depending on each specified area, image processing parameter(e.g., a color correction coefficient, a space filter, or a gradationconversion table) optimal for each original G (e.g., a character, asilver salt photograph (a printing paper), a printed original, an inkjet, a highlight pen, a map, a thermal transfer original).

The scanner gamma conversion section 703 converts a read signal from thescanner section 300 from reflectivity data to color brightness data tostore the data in the image memory 704. The image memory 704 stores theimage signal after the scanner gamma conversion to output a signal tothe MTF filter 707 via the image separation section 70 and the I/F 706.The image separation section 705 determines a character part and aphotograph part of the original G and determines a chromatic part and anachromatic part to output the determination result to the MTF filter707.

The MTF filter 707 performs processing for changing the frequencycharacteristic of an image signal (e.g., edge enhancement, smoothing, orthe like for providing a sharp image, a soft image, the like suitablefor preference of a user) and also performs edge enhancement processingdepending on the edge level of an image signal (adaptation edgeenhancement processing). For example, the MTF filter 707 appliesso-called adaptation edge enhancement, in which a character edge issubjected to edge enhancement and a halftone dot image is subjected toedge enhancement, to the respective R, G, and B signals.

Specifically, for example, the MTF filter 707 includes, as shown in FIG.7, a smoothing filter 730, an edge amount detection filter 731, aLaplacian filter 732, a smoothing filter 733, a table conversion 734, anintegrator 735, and an adder 736. The smoothing filter 730 smoothes animage signal, which is converted by the scanner gamma conversion section703 from a reflectivity linear signal to a brightness linear signal,using the coefficients as described below to output the signal as animage signal A to the Laplacian filter 732 and the adder 736.

TABLE 1 ( 1/18)x 0 1 2 1 0 1 2 4 2 1 0 1 2 1 0

The 3×3 Laplacian filter 732 uses a filter shown in FIG. 8 extract adifferential component of image data and outputs the component as theimage signal B to the integrator 735.

Among 10 bit image signals that are not subjected to the gammaconversion by the scanner gamma conversion section 703, for example, ahigher-order 8 bit component is input to the edge amount detectionfilter 731. The edge amount detection filter 731 uses a sub-scanningdirection edge detection filter shown in FIG. 9A, a main scanningdirection edge detection filter shown in FIG. 9B, and an obliquedirection detection filter shown in FIG. 9C and FIG. 9D to perform edgedetection and output a maximum value among detected edge amounts as anedge level to the smoothing filter 733.

The smoothing filter 733 smoothes an edge level detected by the edgeamount detection filter 731 by using, for example, the coefficientsshown below to reduce an influence of a difference in sensitivitybetween even number pixels and odd number pixels of the scanner section300 and output the edge level to the table conversion circuit 734.

TABLE 2 (¼)x 1 2 1

The table conversion circuit 734 subjects the calculated edge level totable conversion to output the edge level as the image signal C to theintegrator 735. In this case, the table conversion circuit 734 uses atable value to specify density of a line or a point (including contrastand concentration) and smoothness of a halftone dot part. An example ofthe table is shown in FIG. 10. The edge level is maximum when a blackline or point is placed in a white background and is smaller when apixel boundary is smoother (e.g., a fine-printed halftone dot, a silversalt photograph, or a thermal transfer original).

The integrator 735 obtains a product of the edge level converted by thetable conversion circuit 734 (the image signal C) and an output value ofthe Laplacian filter 732 (the image signal B) to output the product asan image signal D to the adder 736. The adder 736 adds the image signalafter the smoothing processing (the image signal A) to the image signalD to output a resultant signal as an image signal E to the huedetermination circuit 708 and the color conversion UCR processingcircuit 709 serving as an image processing circuit in a later stage.

The color conversion UCR processing circuit 709 includes a colorcorrection processing section that corrects a difference between a colorseparation characteristic of an input system and a spectralcharacteristic of color materials of an output system to calculate anamount of color materials Y, M, and C required for faithful colorreproduction and a UCR processing section for replacing a part where thethree colors of Y, M, and C are superposed with K (black). A method forthe color correction processing is described with reference to colorspace diagrams in FIGS. 11 to 13.

As shown in FIG. 11, the color correction processing is performed bydividing color spaces (R, G, and B) on a plane radially expanding aroundan achromatic axis (R=G=B(=N axis)). A saturation changes along a T axisprovided to be vertical to the N axis. A hue changes along a rotationdirection U around the N axis in a plane parallel to the T axis.Specifically, in the predetermined rotation direction U, all points on aplane formed to be parallel to the N axis are points showing colordetermined by the rotation direction U.

Points C, M, and Y are points where the saturation is maximized inprimary colors of C, M, and Y of the printer, respectively. Points R, G,and B are points where the saturation is maximized in secondary colorsof R, G, and B of the printer, respectively. The printer colorreproduction area 672 is a substantially spherical area formed byconnecting these points C, M, Y, R, G, and B with a point W and a pointK with a curve. An inner side of this printer color reproduction area672 is an area of a color that can be output by the printer. The signalcolor area 660 is an area of a color that could be taken by a signalcolor with respect to a color image signal.

Note that the image processing apparatus recognizes, to simplifyprocessing in correcting a signal color in this color space, the printercolor reproduction area 670 as the printer color reproduction area 672.The printer color reproduction area 670 is a dodecahedron-like areaformed by connecting the points C, M, Y, R, G, and B, and the point Wand the point K corresponding to maximum values of eight colors with astraight line. Note that, by recognizing the printer color reproductionarea 670 as the printer color reproduction area 672 as described above,no error occurs in a correction amount X.

A hue area is explained with reference to FIG. 12 and FIG. 13. FIG. 12and FIG. 13 show a color space divided into a plurality of hue areas. AC boundary surface 633 is a plane defined by the points C, W, and K.Similarly, “i” boundary surfaces 634 to 638 (i=M, Y, R, G, and B) areplanes defined by the points i, W, and K (i=M, Y, R, G, and B),respectively. The color space is divided by these boundary surfaces 633to 638. The color spaces divided by these boundary surfaces 633 to 638include a CB hue area 640, a BM hue area 641, a MR hue area 642, a RYhue area 643, a YG hue area 644, and a GC hue area 645.

A method of determining a hue of image data using the hue determinationcircuit 708 is explained. First, a hue determination method for athree-dimensional space is explained. Then, a hue determination methodfor a two-dimensional color plane is explained.

In the hue determination method for a three-dimensional space, each hueevaluation value Fx is calculated based on image data to determine,based on a hue evaluation value Fx, a hue area code of a hue areaincluding a signal color.

A theoretical method of deriving the hue evaluation value Fx isexplained. Color coordinates representing the points C, M, Y, R, G, B,W, and K in FIG. 11 are represented as (Dir, Dig, Dib) (i=c, m, y, r, g,b, w, and k).

For example, color coordinates corresponding to the point C are (Dcr,Dcg, Dcb). In this case, the C boundary surface 633 is represented by,for example, Equations 1 to 6 below.(Dcg−Dcb)*Dr+(Dcb−Dcr)*Dg+(Dcr−Dcg)*Db=0  (1)(Dmg−Dmb)*Dr+(Dmb−Dmr)*Dg+(Dmr−Dmg)*Db=0  (2)(Dyg−Dyb)*Dr+(Dyb−Dyr)*Dg+(Dyr−Dyg)*Db=0  (3)(Drg−Drb)*Dr+(Drb−Drr)*Dg+(Drr−Drg)*Db=0  (4)(Dgg−Dgb)*Dr+(Dgb−Dgr)*Dg+(Dgr−Dgg)*Db=0  (5)(Dbg−Dbb)*Dr+(Dbb−Dbr)*Dg+(Dbr−Dbg)*Db=0  (6)

A color space is divided, for example, by the boundary surface 633 intotwo areas, an area including the CB hue area 640 and an area includingthe GC hue area 645. Similarly, the color space is divided to two areasby the respective boundary surfaces 634 to 638. Thus, it is possible todetermine which hue area includes a color image signal based on whicharea of two areas formed by the respective boundary surfaces 633 to 638includes the color image signal. It is possible to determine a hue areaincluding the color image signal based on plus and minus of a valueobtained by substituting the color image signals (Dr, Dg, and Db) inEquations 1 to 6. Thus, the hue evaluation value Fx is determined basedon Equations 1 to 6. The left sides of Equations 1 to 6 are assumed tobe Fc, Fm, Fy, Fr, Fg, and Fb, respectively.

Therefore, in the hue determination for a three-dimensional space, therespective hue evaluation values Fx determined in Equations 7 to 12below are calculated.Fc=(Dcg−Dcb)*Dr+(Dcb−Dcr)*Dg+(Dcr−Dcg)*Db  (7)Fc=( Dmg−Dcm)*Dr+(Dmb−Dmr)*Dg+(Dmr−Dmg)*Db  (8)Fc=(Dyg−Dyb)*Dr+(Dyb−Dyr)*Dg+(Dyr−Dyg)*Db  (9)Fc=(Drg−Drb)*Dr+(Drb−Drr)*Dg+(Drr−Drg)*Db  (10)Fc=(Dgg−Dgb)*Dr+(Dgb−Dgr)*Dg+(Dgr−Dgg)*Db  (11)Fc=( Dbg−Dbb)*Dr+(Dbb−Dbr)*Dg+(Dbr−Dbg)*Db  (12)

For example, when Fc and Fg calculated at arbitrary points (Dr, Dg, Db)in a color space satisfy a condition “Fc≦0 and Fb>0”, this point isincluded in the CB hue area, as it is seen from the table shown below.

TABLE 3 Conditions for hue evaluation coefficients Hue area codes Fc ≦ 0and Fb > 0 0{CB hue area} Fc ≦ 0 and Fm > 0 1{BM hue area} Fm ≦ 0 andFr > 0 2{MR hue area} Fr ≦ 0 and Fy > 0 3{RY hue area} Fy ≦ 0 and Fg > 04{YG hue area} Fg ≦ 0 and Fg > 0 5{GC hue area}As described above, each hue area is defined by the hue evaluation valueFx. The conditions for hue evaluation value Fx associated with the huearea codes in the hue area code table shown in Table 3 are conditionsdetermined by the equations.

Note that, although the hue area code table shown in Table 3 includescolor coordinates on the N axis in the GC hue area for convenience, thecolor coordinates may be included in other hue areas. The hue evaluationvalue Fx changes depending on an actual value of (Dir, Dig, Dib) (i=c,m, y, r, g, b, w, k). Thus, conditions for hue evaluation values to beassociated with the respective hue area codes in the hue area code table(Table 8) may be changed depending on a hue evaluation value.

A method of mapping a three-dimensional color space to a two-dimensionalplane to use a color coordinate of a color image signal in atwo-dimensional plane to determine the hue area including the colorimage signal is explained based on a color plane diagram in FIG. 14 anda flowchart in FIG. 15 with respect to operations of the huedetermination circuit 708.

In the flowchart shown in FIG. 15, first, when a color image signal isinput to the hue determination circuit 708, a value of the color imagesignal is two-dimensionalized (S251). The value of the color imagesignal is substituted in the following Equation to obtain a differenceGR and a difference BG.GR=Dg−Dr  (13)BG=Db−Dg  (14)Consequently, values (Dr, Dg, Db) in a color space of the color imagesignal are converted the values (GR, BG) in a color plane.

FIG. 14 is a schematic of a two-dimensional plane to which a color imagesignal should be mapped. In this two-dimensional plane, a straight linecorresponding to “Dg−Dr” is assumed to be the GR axis and a straightline corresponding to “Db−Dg” is assumed to be the BG axis. The GR axisand the BR axis are orthogonal to each other.

The points (Dr, Dg, Db) on the color space are mapped to the color planeshown in FIG. 14 by a Equation below. The points (Dnr, Dng, Dnb) on theN axis in the color space are mapped to the (Dng−Dnr, Dnb−Dng) in thecolor plane shown in FIG. 14. Since Dnr=Dng=Dnb is established, Equation15 below is obtained.(Dng−Dnr, Dnb·Dng)=(0,0)  (15)

All points on the N axis are mapped to the origin n in the plane shownin FIG. 14. The points C, M, Y, R, G, and B in the color space arearranged around the origin n as shown in FIG. 14. Thus, six hue areas640 to 645 shown in FIG. 12 are mapped to areas 740 to 745 in the colorplane that are divided by straight lines connecting the N axis to thepoints C, M, Y, R, G, and B, respectively.

Based on the respective color values of the input color image signal,the difference GR, the difference BG, and each hue evaluation value Fx′(x=c, m, y, r, g, b) are calculated (S252). Based on the respective hueevaluation value Fx′, difference GR, and difference BG, the hue areacode table shown in the Table 4 below is used to determine a hue areacode of a hue area including a signal color (S253).

A method of deriving the hue evaluation value Fx′ is explained. In thecolor plane shown in FIG. 14, the straight lines connecting the point Nto the points C, M, Y, R, G, and B (i.e., straight line NC, straightline NM, straight line NY, straight line NR, straight line NG, andstraight line NB) are represented as follows, respectively.BG=(Dcb−Dcg)/(Dcg−Dcr)*GR (where Dcg−Dcr≠0)  (16)BG=(Dmb=Dmg)/(Dmg−Dmr)*GR (where Dmg−Dmr≠0)  (17)BG=(Dyb−Dyg)/(Dyg−Dyr)*GR (where Dyg−Dyr≠0)  (18)BG=(Drb−Drg)/(Drg−Drr)*GR (where Drg−Drr≠0)  (19)BG=(Dgb−Dgg)/(Dgg−Dgr)*GR (where Dgg−Dgr≠0)  (20)BG=(Dbb−Dbg)/(Dbg−Dbr)*GR (where Dbg−Dbr≠0)  (21)

From a magnitude relation between the BG value obtained by substitutingthe GR value of the color image signal and the actual BG value of thecolor image signal in respective Equations 16 to 21, a positionalrelation between a straight line determined by each Equation and a pointcorresponding to a color image signal are seen. Thus, it is possible todetermine which hue area includes the color image signal based on themagnitude relation between the BG value obtained by substituting the GRvalue of the color image signal in Equations 16 to 21 and the BG valueof the color image signal.

Thus, based on Equations 16 to 21, the hue evaluation value Fx′ isdetermined in the manner as described below.Fc′=(Dcb−Dcg)/(Dcg−Dcr)*GR  (22)Fm′=(Dmb−Dmg)/(Dmg−Dmr)*GR  (23)Fy′=(Dyb−Dyg)/(Dyg−Dyr)*GR  (24)Fr′=(Drb−Drg)/(Drg−Drr)*GR  (25)Fg′=(Dgb−Dgg)/(Dgg−Dgr)*GR  (26)Fb′=(Dbb−Dbg)/(Dbg−Dbr)*GR  (27)Equations 22 to 27 are obtained by changing the left sides of Equations16 to 21 to Fc′, Fm′, Fy′, Fr′, Fg′, and Fb′.

For example, when Fc′ and Fb′ calculated from an arbitrary point (GR,BG) in a color plane satisfy a condition “BG≦Fc′ and BG>Fb′”, it is seenfrom a table below that this point is included in the CB hue area.

TABLE 4 Conditions for hue evaluation coefficients Fx′ Hue area codescode BG ≦ fc′ and BG > fb′ 0{CB part color space} BG ≦ fb′ and BG > fm′1{BM part color space} BG ≦ fm′ and BG > fr′ 2{MR part color space} BG ≦fr′ and BG > fy′ 3{RY part color space} BG ≦ fy′ and BG > fg′ 4{YG partcolor space} BG ≦ fg′ and BG ≧ fc′ 5{GC part color space}Conditions for hue evaluation value Fx′ in the hue area code table shownin Table 4 that are associated with hue area codes are conditionsdetermined based on the equation. In this way, the conditions for thehue evaluation value Fx′ are set in the hue area code table of Table 4in advance. Thus, the hue determination circuit 708 only has to specify,from the conditions for the hue evaluation value Fx′ associated with therespective hue area codes as shown in the hue area code table of Table4, conditions satisfied by the BG and the hue evaluation value Fx′ toselect, in the hue area code table (Table 4), a hue area codecorresponding to this condition. FIG. 16 is the color plane diagram inFIG. 14 associated with a hue area.

In the hue area code table shown in Table 4, the color coordinates onthe N axis are included in the GC hue area. However, the colorcoordinates may be included in other hue areas.

The hue evaluation value Fx′ changes depending on an actual value of(Dir, Dig, Dib) (i=c, m, y, r, g, b, w, and k). Therefore, in the huearea code table (Table 4), conditions of a hue evaluation value thatshould be associated with each hue area code may be changed depending ona value of the hue evaluation value Fx′.

Note that, although the conversion equation shown in Equations 13 and 14are used to convert the color image signal (Dr, Dg, Db) to the value(GR, BG) in the color plane, the color image signal may be converted byEquations 28 and 29 below.GR=Ri·Dr+Gi·Dg+Bi·Db  (28)BG=Rj·Dr+Gj·Dg+Bj·Db  (29)where Ri=Gi=Bi=0 and Rj=Gj=Bj=0.

As described above, it is judged by the hue determination circuit 708 towhich part in the divided spaces the input image signal (R, G, B)belongs. Thereafter, masking coefficients set in advance for therespective spaces are used to perform a color correction processing withthe following Equation (30) (a color correcting unit).

$\begin{matrix}{\begin{pmatrix}{Y({hue})} \\{M({hue})} \\{C({hue})} \\{K({hue})}\end{pmatrix} = {\begin{pmatrix}{{aYB}({hue})} & {{aYG}({hue})} & {{aYR}({hue})} & {{aY}({hue})} \\{{aMB}({hue})} & {{aMG}({hue})} & {{aMR}({hue})} & {{aM}({hue})} \\{{aCB}({hue})} & {{aCG}({hue})} & {{aCR}({hue})} & {{aC}({hue})} \\{{aKB}({hue})} & {{aKG}({hue})} & {{aKR}({hue})} & {{aK}({hue})}\end{pmatrix}\begin{pmatrix}{B({hue})} \\{G({hue})} \\{R({hue})} \\1\end{pmatrix}}} & (30)\end{matrix}$In that case, linear processing for a masking coefficient (e.g.,concentration adjustment or color balance adjustment) is performed asrequired. Note that, in the following description, a division pointrefers to a point where a boundary surface intersects with a side (e.g.,point G (Green) in FIG. 11). In one example, when the hue is G (Green),the following Equation 31 is obtained.

$\begin{matrix}{\begin{pmatrix}{Y(G)} \\{M(G)} \\{C(G)} \\{K(G)}\end{pmatrix} = {\begin{pmatrix}{{aYB}(G)} & {{aYG}(G)} & {{aYR}(G)} & {{aY}(G)} \\{{aMB}(G)} & {{aMG}(G)} & {{aMR}(G)} & {{aM}(G)} \\{{aCB}(G)} & {{aCG}(G)} & {{aCR}(G)} & {{aC}(G)} \\{{aKB}(G)} & {{aKG}(G)} & {{aKR}(G)} & {{aK}(G)}\end{pmatrix}\begin{pmatrix}{B(G)} \\{G(G)} \\{R(G)} \\1\end{pmatrix}}} & (31)\end{matrix}$

The left side P (hue) (P=C, M, Y, K; hue=hues R, G, B, Y, M, C, K, Wetc) is referred to as a printer vector, the right side S (hue)(S=B, G,R; hue=hues R, G, B, Y, M, C, K, W etc) is referred to as a scannervector, and aPS (hue) (P=C, M, Y, K; S=B, G, and R) is referred to as alinear masking coefficient for each hue.

Usually, a linear masking coefficient aPS (hue) (P=Y, M, C, K; S=R, G,B, constant) of each space is calculated by calculation described belowby determining in advance the R,G,B values at four points, that is,different two points (R1, G1, B1) and (R2, G2, B2) on an achromatic axisas shown in FIG. 13 and two points (R3, G3, B3) and (R4, G4, B4) on 2boundary surfaces not on the achromatic axis, and recording values ofdevelopment sections C, M, Y, and K optimal for the color reproduction(C1, M1, Y1, K1), (C2, M2, Y2, K2), (C3, M3, Y3, K3), and (C4, M4, Y4,K4).

$\begin{matrix}{\begin{pmatrix}{{aYB}\left( {3\; - \; 4} \right)} & {{aYG}\left( {3\; - \; 4} \right)} & {{aYR}\left( {3 - \; 4} \right)} & {{aY}\left( {3\; - \; 4} \right)} \\{{aMB}\left( {3\; - \; 4} \right)} & {{aMG}\left( {3\; - \; 4} \right)} & {{aMR}\left( {3\; - \; 4} \right)} & {{aM}\left( {3\; - \; 4} \right)} \\{{aCB}\left( {3\; - \; 4} \right)} & {{aCG}\left( {3\; - \mspace{11mu} 4} \right)} & {{aCR}\left( {3\; - \; 4} \right)} & {{aC}\left( {3\; - \; 4} \right)} \\{{aKB}\left( {3\; - \; 4} \right)} & {{aKG}\left( {3\; - \mspace{11mu} 4} \right)} & {{aKR}\left( {3\; - \; 4} \right)} & {{aK}\left( {3\; - \; 4} \right)}\end{pmatrix} = {\left( {\begin{matrix}{Y(1)} & {Y(2)} & {Y(3)} \\{M(1)} & {M(2)} & {M(3)} \\{C(1)} & {C(2)} & {C(3)} \\{K(1)} & {K(2)} & {K(3)}\end{matrix}^{\;}\begin{matrix}{Y(4)} \\{M(4)} \\{C(4)} \\{K(4)}\end{matrix}} \right)\begin{pmatrix}{B(1)} & {B(2)} & {B(3)} & {B(4)} \\{G(1)} & {G(2)} & {G(3)} & {G(4)} \\{R(1)} & {R(2)} & {R(3)} & {R(4)} \\{\; 1} & 1 & 1 & 1\end{pmatrix}^{- 1}}} & (32)\end{matrix}$Equation 32 is obtained by multiplying

$\begin{matrix}{\begin{pmatrix}{Y(1)} & {Y(2)} & {Y(3)} & {Y(4)} \\{M(1)} & {M(2)} & {M(3)} & {M(4)} \\{C(1)} & {C(2)} & {C(3)} & {C(4)} \\{K(1)} & {K(2)} & {K(3)} & {K(4)}\end{pmatrix} = {\begin{pmatrix}{{aYB}\left( {3\; - \mspace{11mu} 4} \right)} & {{aYG}\left( {3\; - \mspace{11mu} 4} \right)} & {{aYR}\left( {3\; - \; 4} \right)} & {{aY}\left( {3 - \; 4} \right)} \\{{aMB}\left( {3\; - \; 4} \right)} & {{aMG}\left( {3\; - \; 4} \right)} & {{aMR}\left( {3\; - 4} \right)} & {{aM}\left( {3\; - 4} \right)} \\{{aCB}\left( {3\; - \mspace{11mu} 4} \right)} & {{aCG}\left( {3\; - \; 4} \right)} & {{aCR}\left( {3 - \; 4} \right)} & {{aC}\left( {3\; - \; 4} \right)} \\{{aKB}\left( {3\; - \mspace{11mu} 4} \right)} & {{aKG}\left( {3\; - \; 4} \right)} & {{aKR}\left( {3 - \; 4} \right)} & {{aK}\left( {3\; - 4} \right)}\end{pmatrix}\begin{pmatrix}{B(1)} & {B(2)} & {B(3)} & {B(4)} \\{G(1)} & {G(2)} & {G(3)} & {G(4)} \\{R(1)} & {R(2)} & {R(3)} & {R(4)} \\1 & 1 & 1 & 1\end{pmatrix}}} & (33) \\\begin{pmatrix}{B(1)} & {B(2)} & {B(3)} & {B(4)} \\{G(1)} & {G(2)} & {G(3)} & {G(4)} \\{R(1)} & {R(2)} & {R(3)} & {R(4)} \\1 & 1 & 1 & 1\end{pmatrix} & (34)\end{matrix}$which is an inverse matrix of

$\left( \begin{matrix}\left. \begin{matrix}{B(1)} & {B(2)} & {B(3)} & {B(4)} \\{G(1)} & {G(2)} & {G(3)} & {G(4)} \\{R(1)} & {R(2)} & {R(3)} & {R(4)} \\1 & 1 & 1 & 1\end{matrix} \right)^{- 1} & (35)\end{matrix} \right.$and replacing both sides.

In Equation 33, aXY(3-4) represents a masking coefficient established ina color area between the hue 3 and the hue 4. Recording values of C, M,Y, and K at the respective points are equivalent achromaticconcentration conversion values before the UCR.

Note that, to simplify the explanation, it is assumed that two points onan achromatic axis are a white point and a black point. In this case,when a maximum value taken by the equivalent achromatic concentrationconversion value is assumed to be Xmax, the respective values have therelations as shown below.

In the case of a white point: R1=G1=B1=C1=M1=Y1=0≧K1

In the case of a black point: R1=G1=B1=C1=M1=Y1=Xmax≧K2

It is preferable that two points on the boundary surface are pointswhere the minimum values of the recording values of the developmentsections C, M, Y, and K are 0 and the maximum value of the recordingvalue are Xmax (i.e., a point that can be recorded on each boundarysurface and that has the highest saturation). The following conditionsare established.Min(C3,M3,Y3)=0≧K3Max(C3,M3,Y3)=XmaxMin(C4,M4,Y4)=0≧K4Max(C4,M4,Y4)=Xmax

It is also possible to control a UCR ratio by determining a recordingvalue of the development section K from a minimum value among theminimum values of the development sections C, M, and Y in the manner asdescribed below.

In the case of the UCR ratio of 100%: K=Min(C, M, Y) In the case of theUCR ratio of 70%: K=Min(C, M, Y)×0.7

When the color space (R, G, B) is divided by 6 boundary surfaces asshown in FIG. 11, the R, G, and B values at eight points, that is, atleast six points on each boundary surface and two points on theachromatic axis and recording values of C, M, Y, and K of developmentsections optimal for the reproduction of the color, are determined inadvance. Based on the values, masking coefficients of the respectivespaces are calculated. Note that, it is possible to calculate themasking coefficients of the respective spaces in advance as describedabove, store the masking coefficients in a ROM, RAM, or the like, andselect an appropriate masking coefficient according to a color judged inthe hue judgment to perform color correction to perform a colorcorrection in color correction processing.

On the other hand, the color conversion UCR processing circuit 709performs a calculation using the following equation to perform a colorcorrection processing.Y′=Y−α*min(Y,M,C)M′=M−α*min(Y,M,C)C′=C−α*min(Y,M,C)Bk=α*min(Y,M,C)

In the equation, α denotes a coefficient that determines amount of UCRand, when α is 1, a 100% UCR processing is obtained. The value α may bea fixed value. For example, α is set close to 1 in a high concentrationpart and is set close to 0 in a highlight part (a low imageconcentration section) to smooth an image in the highlight part.

The masking coefficients are different for each of fourteen hues, thatis, twelve hues obtained by further evenly dividing six hues of R, G, B,Y, M, and C, respectively, and black and white.

The hue determination circuit 708 determines to which hue an image dataread by the scanner section 300 belongs to output a result of thedetermination to the color conversion UCR processing circuit 709.

Based on the determination result of the hue determination circuit 708,the color conversion UCR processing circuit 709 selects maskingcoefficients for the respective hues to perform the color correctionprocessing.

The enlargement/reduction circuit 711 subjects the image data after thecolor correction processing to vertical and horizontalenlargement/reduction. The image processing (create) circuit 712subjects the image data after the enlargement/reduction processing torepeat processing or the like to output a result the processing to theimage processing printer gamma conversion circuit 713.

The image processing printer gamma conversion circuit 713 can alsoperform, according to the image quality mode (e.g., character,photograph), correction of an image signal while simultaneouslyperforming a background skip or the like. The image processing printergamma conversion circuit 713 has a plurality of gradation conversiontables (image signal conversion tables) (e.g., ten tables) that can beswitched according to an area signal generated by the image processingcircuit 712 to select a gradation conversion table optimal for eachoriginal (e.g., a character, a silver salt photograph (printing paper),a printed original, ink jet, a highlight pen, a map, or a thermaltransfer original) from a plurality of image processing parameters,correct an image signal depending on the image quality mode, and outputthe result to the gradation processing circuit 714.

The gradation processing circuit 714 subjects the image data input fromthe image processing printer gamma conversion circuit 713 to ditherprocessing to output a result of the processing to the interfaceselector 721 of the printer section 100.

The gradation processing circuit 714 can select dither processing of anarbitrary size from a 1×1 no-dither processing to dither processing bym×n pixels (m and n are positive integers). For example, the gradationprocessing circuit 714 performs dither processing using up to thirty-sixpixels. The size of a dither processing using all of thirty-six pixelsincludes, for example, 6 pixels in the main scanning direction×6 pixelsin the sub-scanning direction (total thirty-six pixels) or 18 pixels inthe main scanning direction×2 pixels in the sub-scanning direction(total thirty-six pixels).

FIG. 17A is a schematic of an example in which 6 pixels in the mainscanning direction×6 pixels in the sub-scanning direction (totalthirty-six pixels) are used for the dither processing. FIG. 17B is aschematic of an example of an index table that records correspondencebetween respective pixels and gradation table numbers adapted to thepixels. FIGS. 18A to 18C are schematics of examples of the gradationprocessing table (a dither table) of 2 pixels in the main scanningdirection×2 pixels in the sub-scanning direction.

The gradation processing circuit 714 stores the index table and thegradation processing table in a temporary memory referred to as aninternal resistor. Values for the respective tables are set according tocontrol of the CPU 715.

In the gradation processing tables of FIGS. 18A to 18C, the horizontalaxis represents an image signal input to a pixel while the vertical axisrepresents an output value from the pixel. FIG. 18A is a diagram ofthree gradation processing tables of T1, T2, and T3. FIG. 18B is adiagram of gradation processing tables of T1 to T5. The gradationprocessing tables of T1 and T2 are common to those in FIG. 18A but thegradation processing tables of T4 and T5 are different from those inFIG. 18A. FIG. 18C is a diagram of gradation processing tables of T6,T7, and T3. The gradation processing table of T3 is common to that ofFIG. 18A.

In FIG. 17A, when values of the pixel numbers are set such that thepixel numbers are shifted by one pixel in the main scanning direction(FIG. 19A), an index table as shown in FIG. 19B is obtained. Althoughnot shown in the figure, the values may set such that the pixel numbersare shifted in the sub-scanning direction. The values of the shiftamount of the pixel numbers in the main scanning direction and the shiftamount of the pixel numbers in the sub-scanning direction may be set toset a gradation processing in which different screen angles are set forthe respective colors of Y, M, C, and K.

FIG. 20 is a schematic of an index table corresponding to dither of 2pixels in the main scanning direction×2 pixels in the sub-scanningdirection.

In this case, in an output of the gradation processing circuit 714, apixel frequency is reduced to ½. Thus, the image data bus has a width ofsixteen bits (two pieces of image data of eight bits) to be able tosimultaneously transfer data of two pixels to the printer section 100.

Referring back to FIG. 6, the printer section 100 is connected to theIPU 612 by the I/F selector 721 as described above. The I/F selector 721has a switching function to output the image data read by the scannersection 300 for processing by an external image processing apparatus orthe like or to allow the printer section 100 to output the image datafrom an external host computer 740 or an image processing apparatus.Note that the image data from the external host computer 740 is input tothe I/F selector 721 via the printer controller 741.

The image formation printer γ (process control γ) correction circuit 723converts the image signal from the I/F selector 721 with a gradationconversion table (an image signal conversion table) to output a resultof the conversion to a laser modulation circuit of the printer engine724.

As described above, it is possible to use the color copying apparatus 1a printer because the image signal from the host computer 740 is inputto the I/F selector 721 via the image signal and subjected to gradationconversion by the image formation printer γ correction circuit 723 andimage formation is performed by the printer engine 724.

The color copying apparatus 1 executes image processing when the CPU 715uses the RAM 717 as a work memory based on a program in the ROM 716 tocontrol the respective sections of the IPU 612. When the CPU 715 isconnected to the system controller 600 via the serial I/F to receive acommand from the operation section 500 or the like (e.g., an imagequality mode, concentration information, or area information) via thesystem controller 600, the CPU 715 sets various parameters in the IPU612 based on the image quality mode, the concentration information, thearea information, or the like to perform the image processing.

The pattern generation section 710 of the IPU 612 and the patterngeneration section 722 of the printer section 100 generate gradationpatterns to be used by the IPU 612 and the printer section 100,respectively.

The area processing section 702 generates, as described above, an areasignal to differentiate a currently-processed image data correspondingto an area in the original G. This area signal is used to switch aparameter used for image processing in a later stage. It is possible torepresent a concept of the area processing by this area processingsection 702 as shown in FIG. 21. In FIG. 21, with respect to image dataobtained by reading the original G having a plurality of areas (e.g., acharacter area (an area 0), a printing paper area (an area 1), and anink jet area (an area 2)) with the scanner section 300, the areaprocessing section 702 compares specified area information (areainformation) on the original G with read position information duringimage reading to generate an area signal. As in the description for theimage processing printer gamma conversion circuit 713 and the gradationprocessing circuit 714 in FIG. 21, the IPU 612 changes, based on thisarea signal from the area processing section 702, parameters used by thescanner gamma conversion section 703, the MTF filter 707, the colorconversion UCR processing circuit 709, the image processing circuit 712,the image processing printer gamma conversion circuit 713, and thegradation processing circuit 714.

For example, the image processing printer gamma conversion circuit 713decodes an area signal from the area processing section 702 with adecoder and uses a selector to select a table from a plurality ofgradation conversion tables (e.g., a character (table 1), ink jet (table2), printing paper (table 3), printing (table 4)). In the example of theoriginal G in FIG. 21, the character area 0, the printing paper area 1,and the ink jet area 2 are provided. The image processing printer gammaconversion circuit 713 selects the character gradation conversion table1 for the character area 0, the printing paper gradation conversiontable 3 for the printing paper area 1, and the ink jet gradationconversion table 2 for the ink jet area 2.

Based on the signal obtained by decoding the area signal with thedecoder again, the gradation processing circuit 714 uses the selector 2to switch, with respect to the image signal subjected to the gradationconversion by the image processing printer gamma conversion circuit 713,gradation processing (e.g., processing without using a dithering,processing using dither, and error diffusion processing). Note that thegradation processing circuit 714 subjects the ink jet original G and theink jet area of the original G to error diffusion processing.

The gradation processing circuit 714 uses the decoder to select a line 1or a line 2 for the image signal after the gradation processing based onthe read position information. This selection of the line 1 or the line2 is switched for every different one pixel in the sub-scanningdirection. The gradation processing circuit 714 temporarily stores thedata for the line 1 in a first in First out (FIFO) memory located at thedownstream of the selector and outputs the data for the line 1 and line2 to reduce the pixel frequency to ½ and output the data to the I/Fselector 721.

In the color copying apparatus 1, the laser optical system 106 of theprinter section 100 includes a laser modulation circuit 120 as shown inFIG. 22 that includes a lookup table (LUT) 121, a pulse width modulationcircuit (PWM) 122, and a power modulation circuit (PM) 123. In thislaser modulation circuit 120, the writing frequency is 18.6 megahertzand the scanning time for 1 pixel is 53.8 nanoseconds.

8-bit image data is input to the lookup table (LUT) 121. The lookuptable (LUT) subjects the input image data to gamma conversion to outputthe data to the pulse width modulation circuit (PWM) 122. The pulsewidth modulation circuit (PWM) 122 converts the data, based on thehigher-order 3-bit signal of the 8-bit image signal input from thelookup table (LUT) 121, to 8-valued pulse width to output the converteddata to the power modulation circuit (PM) 123. The power modulationcircuit (PM) 123 subjects the data to 32-valued power modulation basedon lower-order five bits. The power modulation circuit (PM) 123 isconnected to a laser diode (LD) 124 and a photo detector (PD) 125. Thepower modulation circuit (PM) 123 causes the laser diode (LD) 124 toemit light based on the modulated signal and monitors, based on amonitor signal from the photo detector (PD) 125, light-emitting strengthof the laser diode (LD) 124 to correct the light-emitting strength foreach dot. It is possible change a maximum value of the strength of thelaser light emitted by this laser diode (LD) 124 to eight bits (256levels) independent of the image signal.

A beam diameter in the main scanning direction with respect to a size ofone pixel of laser light emitted from the laser diode (LD) 124 (the beamdiameter is defined as a width of the beam when the beam strength duringthe stationary status is attenuated to 1/e2 of the maximum value) is 50micrometers in the main scanning direction and 60 micrometers in thesub-scanning direction in 600 DPI and one pixel of 42.3 micrometers.

This laser modulation circuit 120 is prepared in association with piecesof image data of the line 1 and line 2 explained with reference to FIG.21. The pieces of image data of the line 1 and line 2 are synchronizedand are scanned on the photosensitive element drums 104K to 104C inparallel to the main scanning direction.

The scanner section 300 has a circuit block configuration shown in FIG.23 and includes a CCD 312, an amplification circuit 321, a sample hold(S/H) circuit 322, an A/D conversion circuit 323, a black correctioncircuit 324, a CCD driver 325, a pulse generator 326, and a clockgenerator 327.

The scanner section 300 uses the halogen lamp 302 shown in FIG. 3 toemit light to the original G, subjects reflected light from original Gto color separation with an RGB filter of the CCD 312, reads an image ofthe original G with the CCD 312, and outputs an analog image signal fromthe CCD 312. The CCD driver 325 supplies a pulse signal to drive the CCD312. A pulse source required to drive the CCD driver 325 is generated bythe pulse generator 326. The pulse generator 326 generates a pulsesignal using a clock signal oscillated by the clock generator 327 thatincludes a crystal oscillator or the like as a reference signal. The S/Hcircuit 322 supplies a timing signal required for sample-holding animage signal from the CCD 312 to the S/H circuit 322.

The amplification circuit 321 amplifies the analog image signal from theCCD 312 to a predetermined level and outputs the signal to the S/Hcircuit 322. The S/H circuit 322 sample-holds the image signal from theamplification circuit 321 to output the signal to the A/D conversioncircuit 323. The A/D conversion circuit 323 digitizes the analog imagesignal sample-held by the S/H circuit 322 to be, for example, an 8-bitsignal and outputs the signal to the black correction circuit 324. Theblack correction circuit 324 reduces, with respect to the image datasubjected to the digital conversion by the A/D conversion circuit 323,fluctuation in a black level among chips and pixels of the CCD 312(electric signal when the amount of light is small) to prevent the blackpart of the image from having a linear mark or unevenness and outputsthe data to the shading correction circuit 701 of the IPU 612.

As described above, the shading correction circuit 701 corrects thewhite level (electric signal when the amount of light is large) tocorrect, as shown in FIG. 24, the white level by correcting thesensitivity dispersion of an irradiation system, optical system, or theCCD 312 based on the white color data obtained when the scanner section300 is moved to a position of a uniform white reference plate and isirradiated.

An image signal from the shading correction circuit 701 is processed byan image processing section ranging from the area processing section 702of the IPU 612 to the gradation processing circuit 714 and is recordedand output by the printer section 100. The above respective circuits arecontrolled by the CPU 715 based on the program and data in the ROM 716and the RAM 717.

An amplification amount of the amplification circuit 321 is determinedsuch that an output value of the A/D conversion circuit 323 has adesired value with respect to a specific original concentration. Forexample, 240 values in an 8-bit signal value is obtained with anoriginal concentration of 0.05 (0.891 of reflectivity) in a normalcopying operation. In a shading correction, the amplification rate isreduced to increase the sensitivity of the shading correction. This isbecause an amplification ratio in a normal copy is saturated at 255values when reflected light is high and when an image signal toner hasthe size exceeding 255 values in 8-bit signal, causing an error in theshading correction. Specifically, FIG. 25 is a schematic diagram inwhich an image reading signal amplified by the amplification circuit 321sample-held by the S/H circuit 322. In FIG. 25, the horizontal axisrepresents time when the amplified analog image signal passes the S/Hcircuit 322 and the vertical axis represents a magnitude of theamplified analog signal. The analog signal is sample-held by thepredetermined sample hold time shown in FIG. 25 and the signal is sentto the A/D conversion circuit 323. FIG. 25 is a schematic forillustrating the image signal for which the white level is read and theamplified image signal has, for example, 240 values as a value after theA/D conversion during a copy operation and 180 values during a whitecorrection operation.

An effect of the embodiment is described. The color copying apparatus 1of this embodiment executes, in using the linkage output function asdescribed above, at least one scanner calibrations in advance (describedbelow).

The scanner calibration is performed, for example, using a linkage colorcorrection chart HC as shown in FIG. 26 as a calibration referencechart. In this linkage color correction chart HC, hue areas provided tohave a boundary as a plane provided in parallel to a brightness axis ina color space that are color patches of a plurality of differentchromatic patches are originally drawn with colors. However, FIG. 26 asa patent drawing indicates the areas are displayed by white and blackshowing the color difference by different hatchings.

The linkage color correction chart HC is a patch type chart that isprovided as shown in FIG. 26 such that the center has gray patches(black patches) as a plurality of different achromatic patches havingdifferent image concentrations that are provided on a recording medium(e.g., paper) and the left and right sides have a plurality of colorpatches having different hues. Among the two achromatic gray patches inthe center, one is a gradation pattern printed by 3C gray (that is madeachromatic by superimposing Y, M, and C one on top of another) and theother is a gradation pattern printed by black ink only. In the linkagecolor correction chart HC, with respect to the main scanning directionof the scanner section 300, colors are arrange in the following order:white 1 (background), color 1, black 1, black 2, color 2, and white 2(background). By providing the color patch between white (background)and a black patch, it is possible to reduce the influence by flare lightfrom the surrounding patches (particularly black patch). In the case ofthe arrangement, for example, in an order of the white 1 (background),black 1, color 1, black 2, color 2, and white 2 (background), the color1 is influenced by both sides of black patches, causing the scannersection 300 to have a darker read value. To prevent this, the formerarrangement is adopted.

Each patch in the linkage color correction chart HC is formed to have asize that is about four times as large as a patch of the ACC pattern(see FIG. 47) used in the ACC (described later). The reason why thepatch of the linkage color correction chart HC is provided to have alarge size is that the influence from flare light (reflected light froman original surface surrounding the patch) is reduced in the scannersection 300.

As shown in FIG. 26, the linkage color correction chart HC is providedsuch that the patches are concentrated in substantially the center inthe main scanning direction of the scanner section 300. The reason whythe patches are concentrated in substantially the center in the mainscanning direction of the scanner section 300 is that an end of the mainscanning direction of the scanner section 300 tends to be darkercompared to the center. Note that the patches of the linkage colorcorrection chart HC are provided at positions included in a readingrange of an ACC pattern. This is for an easy use of ACC pattern readingcontrol software when an application program is created.

Chromatic color patches are provided as follows. Twelve color patchesare provided by further dividing six hues of Y, R, M, B, C, and G(Yellow, Red, Magenta, Blue, Cyan, Green) to provide twelve colorpatches corresponding to hue division points (e.g., color between Y andYR) of twelve hue masking coefficients (Y, YR, R, RM, M, MB, B, BC, C,CG, G, GY) and additional Y, G, R, and Orange color patches as areference (e.g., for visual evaluation by copy), thereby providing thetotal of 16 color patches. The respective color patches in the linkagecolor correction chart HC have hue angles as shown below when the hueangle h* is b≦h*<360 degrees (deg) with respect to the brightness L*,saturation C*, and hue h*.

Yellow Red (h*=1 deg)

Orange (h*=26 deg)

Red Yellow (h*=47 deg)

Red (h*=54 deg)

Red Magenta (h*=60 deg)

Magenta Red (h*=84 deg)

Magenta Blue (h*=95 deg)

Blue Magenta (h*=139 deg)

Blue Cyan (h*=170 deg)

Cyan Blue (h*=207 deg)

Cyan Green (h*=232 deg)

Green Cyan (h*=277 deg)

Green (h*=291 deg)

Green Yellow (h*=313 deg)

Yellow Green (h*=352 deg)

Yellow (h*=356 deg)

Note that values are examples.

In the scanner calibration, the linkage color correction chart HC shownin FIG. 26 is read. Based on the reading result, first, a scanner gammaconversion table is created such that a machine difference of thescanner sections 300 is corrected.

A procedure for preparing the scanner gamma conversion table in thisscanner calibration is as indicated by the sequence diagram of FIG. 27.

First, when a user or a service person selects the various setting modein the liquid crystal screen 511 of the operation section 500 shown inFIG. 4, the color copying apparatus 1 causes the liquid crystal screen511 to display the various adjustment screen as shown in FIG. 28. Whenthe execution of “scanner calibration” is selected on this variousadjustment screen, the scanner calibration mode is started and theliquid crystal screen 511 is caused to display the scanner calibrationstart screen as shown in FIG. 29. In this scanner calibration mode, theuser or the service person places the linkage color correction chart HCon the contact glass 3 as an original stand to depress the “readingstart” key in the scanner calibration start screen of the liquid crystalscreen 511 shown in FIG. 29 (S1 in FIG. 20).

When the operation section 500 receives an instruction for starting thereading of the linkage color correction chart HC, the color copyingapparatus 1 instructs, as shown by S2 in FIG. 27, a range from thesystem controller 600 to the scanner section 300 to read the linkagecolor correction chart HC. Then, as shown by S3 in FIG. 27, the scannersection 300 executes the reading of the linkage color correction chartHC to obtain the read values of R, G, and B signals with respect to therespective patches of the linkage color correction chart HC. As shown byS4 in FIG. 27, the scanner section 300 transmits the read values of thelinkage color correction chart HC to the IPU 612.

On the other hand, as indicated by S5 in FIG. 27, reading referencevalues (reference data) of the linkage color correction chart HC areread from a nonvolatile RAM (a reference value storing unit) in thesystem controller 600. Then, as shown by S6 in FIG. 27, the values aresent from the system controller 600 to the IPU 612. The color copyingapparatus 1 displays, when the linkage color correction chart HC isbeing read, a screen shown in FIG. 30 that indicates that the reading isbeing performed.

In receiving the read values and reading reference values of the linkagecolor correction chart HC, the IPU 612 calculates, as shown by S7 inFIG. 27, image processing parameter to transmit the calculated parameterto the system controller 600 as indicated by S8 in FIG. 27.

As indicated by S9 in FIG. 27, the system controller 600 stores thereceived parameter in a nonvolatile RAM.

A method of creating the read value color scanner gamma conversion tablebased on the read values of achromatic patches of the linkage colorcorrection chart HC (see FIG. 26) in S7 of the sequence diagram of FIG.27 is described based on a quaternary chart shown in FIG. 31.

In the quaternary chart of FIG. 31, a first quadrant (1) represents arequired scanner gamma conversion table and a horizontal axis representsan input value to the scanner gamma conversion table and a vertical axisrepresents an output after the scanner gamma conversion. In a fourthquadrant (IV), a vertical axis represents a read value of an achromaticpatch and a graph shows a target value (a reference value) for obtainingthe scanner gamma conversion table from the read values of theachromatic patches. In a third quadrant (III), a horizontal axisrepresents a reference value of a read value of an achromatic patch anda graph shows a result of reading an achromatic gray scale patch withthe scanner section 300. A second quadrant (II) represents no conversion(through).

According to the characteristics shown in the quaternary chart in FIG.31, the scanner gamma conversion table for b, b′ of the first quadrantis created from read values a, a′ of the third quadrant.

The target value of the read value shown in the fourth quadrant of thequaternary chart in FIG. 31 may be different target values for R, G, andB components of the scanner gamma conversion table used when theoriginal is copied or may be the same target value.

As described above, the scanner gamma conversion table for correctingthe difference in the scanner sections 300 is created.

FIG. 32 is a flowchart of a scanner calibration processing. The scannercalibration processing calculates determination reference parameters Fx′and masking coefficients of hue areas based on the reading resultobtained by reading the linkage color correction chart HC shown in FIG.26.

First, when the operation section 500 issues an instruction to start thereading of the linkage color correction chart HC, the linkage colorcorrection chart HC (see FIG. 26) is read (step S601) to determinewhether the read value of the linkage color correction chart HC iswithin a predetermined range (step S602).

When the read value is not within the predetermined range (“NO” at stepS602), it is determined that an original other than that in the linkagecolor correction chart HC is placed on the scanner section 300 and acurrent linear masking coefficient value is used (step S603). Theprocessing is completed.

On the other hand, when the read value is within the predetermined range(“YES” at step S602), the scanner gamma conversion table is created(step S604). As described above, the achromatic patch of the linkagecolor correction chart HC is used to create the scanner gamma conversiontable. Consequently, the machine difference of the scanner section 300is reduced.

The scanner gamma conversion table is used to convert the read value andreverse the value (step S605). Read values S[1] of R, G, and Bcomponents of the first patch having 10-bit accuracy are subjected tothe scanner gamma conversion at f(S[1]) and further subjected togradation reversal. Assuming that the value subjected to the gradationinversion is S′[1],S′[I]=S[White]−f(S[I])is obtained. S[1] includes the three components of Red, Green, and Blueand S[White]is a white reference value for R, G, and B. The scannergamma conversion is performed to improve color reproducibility. A valueof a color having high saturation is increased while a value of a colorhaving a low saturation is reduced to make it easy to handle a color.

A hue angle is calculated (step S606). Based on the read values of datafor R, G, and B of the respective patches of the linkage colorcorrection chart HC (Dr,bg,Db)(=Ri, Gi, Bi (i=number of each patch)),Equations 13 to 29 are used to calculate the parameters GR, GB, and Fx′and divide the R, G, and B image data of the read original for each hue.

Linear masking coefficients are calculated (step S607). The linearmasking coefficient is calculated by using the method and the followingEquation 36 to calculate, based on the read values Ri, Gi, and Bi(i=number of each patch) of the respective patches, linear maskingcoefficients for the respective patches.

$\begin{matrix}\begin{matrix}{\begin{pmatrix}{{aYB}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aYG}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aYR}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aY}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} \\{{aMB}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aMG}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aMR}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aM}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} \\{{aCB}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aCG}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aCR}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aC}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} \\{{aKB}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aKG}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aKR}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aK}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)}\end{pmatrix} = {\begin{pmatrix}{Y(1)} & {Y(2)} & {Y(3)} & {Y(4)} \\{M(1)} & {M(2)} & {M(3)} & {M(4)} \\{C(1)} & {C(2)} & {C(3)} & {C(4)} \\{K(1)} & {K(2)} & {K(3)} & {K(4)}\end{pmatrix} \times}} \\\begin{pmatrix}{{B(1)} + {\Delta\;{B(1)}}} & {{B(2)} + {\Delta\;{B(2)}}} & {{B(3)} + {\Delta\;{B(3)}}} & {{B(4)} + {\Delta\;{B(4)}}} \\{{G(1)} + {\Delta\;{G(1)}}} & {{G(2)} + {\Delta\;{G(2)}}} & {{G(3)} + {\Delta\;{G(3)}}} & {{G(4)} + {\Delta\;{G(4)}}} \\{{R(1)} + {\Delta\;{R(1)}}} & {{R(2)} + {\Delta\;{R(2)}}} & {{R(3)} + {\Delta\;{R(3)}}} & {{R(4)} + {\Delta\;{R(4)}}} \\1 & 1 & 1 & 1\end{pmatrix}^{1}\end{matrix} & (36)\end{matrix}$

The method is described specifically. A value obtained by reading apoint on a boundary surface not existing on an achromatic axis with ascanner CCD showing a standard spectral characteristic for example is(Ri, Gi, Bi) (i=hue 1 to 4). When this point is read by another scanner,because of fluctuation in spectral characteristics of the scanner CCDs,this point is read as (Ri′, Gi′, Bi′)(i=hues 1 to 4) different from (Ri,Gi, Bi) (i=hues 1 to 4). As a result, according to Equation (1), therecording values of the development sections C, M, Y, and K are (Ci′,Mi′, Yi′, Ki′)(i=hues 1 to 4). It is possible to represent Equation 32as follows.

$\begin{matrix}{\begin{pmatrix}{Y\left( 1^{\prime} \right)} & {Y\left( 2^{\prime} \right)} & {Y\left( 3^{\prime} \right)} & {Y\left( 4^{\prime} \right)} \\{M\left( 1^{\prime} \right)} & {M\left( 2^{\prime} \right)} & {M\left( 3^{\prime} \right)} & {M\left( 4^{\prime} \right)} \\{C\left( 1^{\prime} \right)} & {C\left( 2^{\prime} \right)} & {C\left( 3^{\prime} \right)} & {C\left( 4^{\prime} \right)} \\{K\left( 1^{\prime} \right)} & {K\left( 2^{\prime} \right)} & {K\left( 3^{\prime} \right)} & {K\left( 4^{\prime} \right)}\end{pmatrix} = {\begin{pmatrix}{{aYB}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aYG}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aYR}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aY}\left( {3^{\prime} - \; 4^{\prime}} \right)} \\{{aMB}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aMG}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aMR}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aM}\left( {3^{\prime} - \; 4^{\prime}} \right)} \\{{aCB}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aCG}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aCR}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aC}\left( {3^{\prime} - \; 4^{\prime}} \right)} \\{{aKB}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aKG}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aKR}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aK}\left( {3^{\prime} - \; 4^{\prime}} \right)}\end{pmatrix}\begin{pmatrix}{B\left( 1^{\prime} \right)} & {B\left( 2^{\prime} \right)} & {B\left( 3^{\prime} \right)} & {B\left( 4^{\prime} \right)} \\{G\left( 1^{\prime} \right)} & {G\left( 2^{\prime} \right)} & {G\left( 3^{\prime} \right)} & {G\left( 4^{\prime} \right)} \\{R\left( 1^{\prime} \right)} & {G\left( 2^{\prime} \right)} & {G\left( 3^{\prime} \right)} & {G\left( 4^{\prime} \right)} \\1 & 1 & 1 & 1\end{pmatrix}}} & (37)\end{matrix}$where approximation is performed as (R(I′)), G(I′), B(f′))=−(R(i)+ΔR(i),G(i)+ΔG(i), B(i)+ΔB(i))(i=hues 1 to 4) to obtain the following Equation.

$\begin{matrix}\begin{matrix}{\begin{pmatrix}{Y\left( 1^{\prime} \right)} & {Y\left( 2^{\prime} \right)} & {Y\left( 3^{\prime} \right)} & {Y\left( 4^{\prime} \right)} \\{M\left( 1^{\prime} \right)} & {M\left( 2^{\prime} \right)} & {M\left( 3^{\prime} \right)} & {M\left( 4^{\prime} \right)} \\{C\left( 1^{\prime} \right)} & {C\left( 2^{\prime} \right)} & {C\left( 3^{\prime} \right)} & {C\left( 4^{\prime} \right)} \\{K\left( 1^{\prime} \right)} & {K\left( 2^{\prime} \right)} & {K\left( 3^{\prime} \right)} & {K\left( 4^{\prime} \right)}\end{pmatrix} = {\begin{pmatrix}{{aYB}\left( {3^{\prime} - \mspace{11mu} 4^{\prime}} \right)} & {{aYG}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aYR}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aY}\left( {3^{\prime} - 4^{\prime}} \right)} \\{{aMB}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aMG}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aMR}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aM}\left( {3^{\prime} - 4^{\prime}} \right)} \\{{aCB}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aCG}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aCR}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aC}\left( {3^{\prime} - 4^{\prime}} \right)} \\{{aKB}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aKG}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aKR}\left( {3^{\prime} - \; 4^{\prime}} \right)} & {{aK}\left( {3^{\prime} - 4^{\prime}} \right)}\end{pmatrix} \times}} \\\begin{pmatrix}{{B(1)} + {\Delta\;{B(1)}}} & {{B(2)} + {\Delta\;{B(2)}}} & {{B(3)} + {\Delta\;{B(3)}}} & {{B(4)} + {\Delta\;{B(4)}}} \\{{G(1)} + {\Delta\;{G(1)}}} & {{G(2)} + {\Delta\;{G(2)}}} & {{G(3)} + {\Delta\;{G(3)}}} & {{G(4)} + {\Delta\;{G(4)}}} \\{{R(1)} + {\Delta\;{R(1)}}} & {{R(2)} + {\Delta\;{R(2)}}} & {{R(3)} + {\Delta\;{R(3)}}} & {{R(4)} + {\Delta\;{R(4)}}} \\1 & 1 & 1 & 1\end{pmatrix}\end{matrix} & (38)\end{matrix}$where ΔRi=kR1 {(R component of current chromatic value of hue i)−(Rcomponent of reference chromatic value of hue i)} ΔGi=kG1 {(G componentof current chromatic value of hue i)−(G component of reference chromaticvalue of hue i)} ΔBi=kB1 {(B component of current chromatic value of huei)−(B component of reference chromatic value of hue i)} Instead of usingan actual read value (Ri′, Gi′, Bi′), a difference between a referencevalue of a chromatic reference patch and a read value is multiplied by apredetermined coefficient kX (X=R, G, and B) and a product is added to ascanner vector consisting of R, G, and B components (Ri, Gi, Bi)(i=1, 2,3, and 4) stored in advance. Note that, when the scanner vector (Ri, Gi,Bi)(i=1, 2, 3, and 4) is the same as a reference patch obtained by thereference value of the linkage color correction chart HC of thechromatic patch and the reference patch providing the read value, thefollowing coefficient is obtained.

KX=1 (X=R, G, B)

In this embodiment, it is possible to select a combination of a presentvalue and a reference value with an operation section described belowaccording to a fluctuation factor of a scanner machine difference.

In the liquid crystal screen 511 of the operation section 500 shown inFIG. 4, when a scanner calibration menu is called up, a scannercalibration screen shown in FIG. 33 is displayed. The scannercalibration screen in FIG. 33 shows keys for setting the combination ofa “reference value” and a “present value”. When a [factory settingvalue] is selected as a reference value or a present value, the factorysetting value serving as a standard read value of the linkage colorcorrection chart HC shown in FIG. 34 is displayed on the liquid crystalscreen 511. When a [read value] is selected as a present value, a readvalue is displayed on the liquid crystal screen 511 as shown in FIG. 35.Note that, it is possible to change a factory setting value shown inFIG. 34 and a read value shown in FIG. 35. Consequently, a referencevalue selecting unit and a present value selecting unit are realized.

For example, with respect to the scanner section 300 having a smalltemporal fluctuation of the read value of the reference patch, a factorysetting value serving as a standard read value of the linkage colorcorrection chart HC is set as a present value and a design value (fixedvalue) in the ROM is set as a reference value. The design value (fixedvalue) is the first chromatic patch read value when the coefficient(Ri), (Gi), and (Bi) values of Equation 38 are determined. As thefactory setting value, the present value is calculated by the chartconsisting of chromatic patches for which the colors are controlled inadvance. When there is fluctuation of colors of the chromatic patches(e.g., lot difference), the coefficient kX (X=R, G, and B) is reduced ininverse proportion to a color difference from the design value. Thecoefficient kX is provided based on a color difference of an L*a*bcomponent of a CIE Lab color difference between the reference patch forwhich ΔE*ii is used for the design of the ii-th patch and the referencepatch used for the adjustment in the factory.

In the case of ΔE*ii≦1 kX=1 (X=R,G,B)

In the case of 1<E*ii≦2 kX=0.75 (X=R,G,B)

In the case of 2<E*ii≦4 kX=0.5 (X=R,G,B)

In the case of 4<E*ii≦8 kX=0.25 (X=R,G,B)

In the case of 8<E*ii kX=0.0 (X=R,G,B)

With respect to the scanner section 300 having a small temporalfluctuation of read values of the reference patch, instead of using thefactory setting value as a present value, a read value of the linkagecolor correction chart HC is used in which a present value is read everytime. The reference value is a design value (a fixed value) stored inthe ROM. The coefficient kX (X=R, G, and B) is calculated as describedabove.

In performing correction using the linkage color correction chart HC inwhich a color of a reference patch used for the design is different inan amount equal to or higher than a predetermined value due to adifference among printing lots, the scanner calibration screen shown inFIG. 36 is used. A standard read value of the linkage color correctionchart HC having a different color is set as a reference value duringmanufacture or in a factory (a factory setting value) and a valueobtained by causing each apparatus to read this linkage color correctionchart HC is used as a present value. The coefficient in this case isset, as shown in FIG. 36, to be a correction coefficient in inverseproportion to fluctuation (a standard error) in the color in theprinting lot. When the standard error of the fluctuation is large, thecoefficient kX (X=R, G, and B) is set to a value close to 0 and, whenthe standard error is small, the coefficient kX (x=R, G, and B) is setto a value equal to or close to 1. Here, a correction coefficientsetting unit is realized.

Note that the liquid crystal screen 511 of the operation section 500 isa touch panel screen in which a setting value to be changed is selectedand then a parameter is input by a numeric keypad and is set by an enterkey.

It is also possible that a personal computer connected via a LAN cable1000 or a personal computer connected via a USB cable, a RS-232C cable,a centronics cable, or the like is caused to display the screens shownin FIG. 34 to FIG. 36 and values are set on line from the personalcomputer on which these screens are displayed.

Since an objective is to calculate the masking coefficient aPS (i−j)(P=Y, M, C, K, S=B, G, R; i,j=1, 2, 3, 4, j=1, 2, 3, 4) for which theleft sides of Equation 32 and 37 is (Y(i), M(i), C(i), K(i))=(Y(I′),M(I′), K(I′)) where hue I=1, 2, 3, and 4, Equation 39 below is obtained.

$\begin{matrix}\begin{matrix}{\begin{pmatrix}{Y(1)} & {Y(2)} & {Y(3)} & {Y(4)} \\{M(1)} & {M(2)} & {M(3)} & {M(4)} \\{C(1)} & {C(2)} & {C(3)} & {C(4)} \\{K(1)} & {K(2)} & {K(3)} & {K(4)}\end{pmatrix} \approx {\begin{pmatrix}{{aYB}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aYG}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aYR}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aY}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} \\{{aMB}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aMG}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aMR}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aM}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} \\{{aCB}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aCG}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aCR}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aC}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} \\{{aKB}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aKG}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aKR}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)} & {{aK}\left( {3^{\prime}\mspace{14mu} 4^{\prime}} \right)}\end{pmatrix} \times}} \\\begin{pmatrix}{{B(1)} + {\Delta\;{B(1)}}} & {{B(2)} + {\Delta\;{B(2)}}} & {{B(3)} + {\Delta\;{B(3)}}} & {{B(4)} + {\Delta\;{B(4)}}} \\{{G(1)} + {\Delta\;{G(1)}}} & {{G(2)} + {\Delta\;{G(2)}}} & {{G(3)} + {\Delta\;{G(3)}}} & {{G(4)} + {\Delta\;{G(4)}}} \\{{R(1)} + {\Delta\;{R(1)}}} & {{R(2)} + {\Delta\;{R(2)}}} & {{R(3)} + {\Delta\;{R(3)}}} & {{R(4)} + {\Delta\;{R(4)}}} \\1 & 1 & 1 & 1\end{pmatrix}\end{matrix} & (39)\end{matrix}$Equation 36 is obtained by multiplying both sides 39 by

$\begin{matrix}\begin{pmatrix}{{B(1)} + {\Delta\;{B(1)}}} & {{B(2)} + {\Delta\;{B(2)}}} & {{B(3)} + {\Delta\;{B(3)}}} & {{B(4)} + {\Delta\;{B(4)}}} \\{{G(1)} + {\Delta\;{G(1)}}} & {{G(2)} + {\Delta\;{G(2)}}} & {{G(3)} + {\Delta\;{G(3)}}} & {{G(4)} + {\Delta\;{G(4)}}} \\{{R(1)} + {\Delta\;{R(1)}}} & {{R(2)} + {\Delta\;{R(2)}}} & {{R(3)} + {\Delta\;{R(3)}}} & {{R(4)} + {\Delta\;{R(4)}\quad}} \\1 & 1 & 1 & {1{\quad\quad}}\end{pmatrix} & (40)\end{matrix}$which is an inverse matrix of

$\begin{matrix}\begin{pmatrix}{{B(1)} + {\Delta\;{B(1)}}} & {{B(2)} + {\Delta\;{B(2)}}} & {{B(3)} + {\Delta\;{B(3)}}} & {{B(4)} + {\Delta\;{B(4)}}} \\{{G(1)} + {\Delta\;{G(1)}}} & {{G(2)} + {\Delta\;{G(2)}}} & {{G(3)} + {\Delta\;{G(3)}}} & {{G(4)} + {\Delta\;{B(4)}}} \\{{R(1)} + {\Delta\;{R(1)}}} & {{R(2)} + {\Delta\;{R(2)}}} & {{R(3)} + {\Delta\;{R(3)}}} & {{R(4)} + {\Delta\;{R(4)}}} \\1 & 1 & 1 & 1\end{pmatrix}^{- 1} & (41)\end{matrix}$

Finally, the read value and the linear masking coefficient are stored ina nonvolatile RAM, RAM, or the like (step S608). The processing iscompleted.

Note that, as shown in the flowchart in FIG. 37, instead of performingstep S604 of the flowchart in FIG. 32 to create the scanner gammaconversion table, a fixed scanner gamma conversion table stored inadvance may be used to convert a chromatic reference patch.

FIG. 38 is a schematic of classes of the scanner calibration. In FIG.38, a color correction coefficient used for copy (resistor value set fora color correction circuit (ASIC)) 801, a linear masking coefficient803, a hue determination parameter 802, a scanner vector 804, a scannerinverse matrix parameter 805, a printer vector 806, an imageconcentration selection 807 (in an operation section), a calibrationdata selection I/F 808 (in an operation section), a linkage colorcorrection chart HC read value (present value) 809 as an object, alinkage color correction chart HC read value (this time value) 810 as anobject, a ROM 811, a nonvolatile RAM (NV-RAM) 812, a linkage colorcorrection chart HC read value (previous value) 813 as an object, and ascanner 814 are shown.

It is possible to calculate the color correction coefficient 801 basedon the hue determination parameter 802 and the linear maskingcoefficient 803. It is possible to calculate the hue determinationparameter 802 based on the scanner vector 804. It is possible tocalculate the linear masking coefficient 803 based on the scannerinverse matrix parameter 8015 and the printer vector 806. It is possibleto calculate the scanner inverse matrix parameter 805 based on thescanner vector 804. The printer vector 806 is selected from the imagequality mode and the concentration selection by the image selection I/F807 of the operation section. The data of the printer vector 806 isstored in the RAM 811. The scanner vector 804 is calculated based on thelinkage color correction chart HC read value (present value) 809 as anobject. According to the calibration data selection I/F 808 (in anoperation section), it is possible to select the linkage colorcorrection chart HC read value (present value) 809 from the linkagecolor correction chart HC read value (previous value) 813 that is readand stored in the NV-RAM 812 in advance and the linkage color correctionchart HC read value (this time value) 810 read from the scanner 814anew. The linkage color correction chart HC read value (present value)809 and the linkage color correction chart HC read value (previousvalue) 813 are stored in the NV-RAM 812.

When the linkage color correction chart HC read value (previous value)813 is desired to be used as the linkage color correction chart HC readvalue (present value) 809, “return to an original value” of the scannercalibration in FIG. 28 is selected. Consequently, the value read andstored in advance is called up and the color correction coefficient 801is recalculated.

Note that a scanner gamma conversion table for the ACC is different fromthe copy (original reading) scanner gamma conversion table in that thesensitivity is high with respect to a spectral reflection factorcharacteristic of toner on transfer paper to be read and the ACC patternreading scanner gamma conversion table is created according to achromatic patch read value of the linkage color correction chart HC suchthat the influence by fluctuation in spectral sensitivities of the CCD312 is corrected.

As described later, based on a chromatic patch and an achromatic patchhaving different tints, an ACC pattern (see FIG. 47) reading scannergamma conversion table is created. The creation is explained withreference to FIG. 39 with a method of creating a yellow toner readingscanner y correction table (scanner gamma conversion table) as anexample.

A chromatic (color) patch used for the correction of yellow toner is theone as shown in FIG. 39. This chromatic patch is an example of a valueobtained by reading a color patch extracted for the correction of yellowtoner by a scanner serving as a reference. When yellow toner is read, ablue signal is used because of the high sensitivity of blue. A bluesignal is used out of different R, G, and B reading signals of 1. white,2. yellow, 5. blue, 6. cyan, 10. gray, and 11. black from a plurality ofchromatic color patches having different tints to create a correctiontable for reading yellow toner.

When the yellow reading correction table at the time of execution of theACC is created, the linkage color correction chart HC is created byprinting ink. Thus, a spectral reflection factor of the chart isdifferent from that of toner. FIG. 39 shows an example of a correctioncoefficient for blue for the difference.

It is possible to calculate this correction coefficient based on FIG. 40that represents the spectral sensitivity of a blue signal of the CCD 312and a spectral reflection factor of yellow toner by wavelength λ. InFIG. 40, the horizontal axis represents the wavelength λ while thevertical axis in the graph (a) represents the spectral sensitivity [%]of the CCD 312 shown in the left side axis and the vertical axes in thegraphs (c) and (d) represent the spectral reflection factor [%] of tonershown in the right side. In FIG. 40, (a) represents a spectralsensitivity of a blue signal filter, (c) represents a spectralreflection factor of a yellow toner, (d) represents a spectralreflection factor of yellow ink, and (d) represents a spectralreflection factor of black (Bk) toner when the deposition amount issmall. The (a) spectral sensitivity is obtained by multiplying thespectral transmission rate of blue filter of the CCD 312 with thespectral energy of the light source (halogen lamp 302).

As it is seen from FIG. 40, an output B of the blue signal (CCD 312,color material) is obtained by integrating the wavelength λ with anintegration value S (CCD, λ)×σ(color material, λ, area ratio) ofspectral sensitivity S (CCD, λ) of the CCD 312 and the color materialspectral reflection factor σ (color material, λ, area ratio). The outputB of the blue signal (CCD 312, color material) is given by the followingEquation 42.B(CCD, color material, area ratio)=∫S(CCD, λ)·σ(color material, λ, arearatio)  (42)

When yellow toner (hereinafter simply referred to as Y toner) and yellowink (hereinafter simply referred to as Y ink) are read, blue signals tothe spectral sensitivity characteristic “a” of the CCD 312 arerepresented by the following Equations 43 and 44.B(a, Y toner, 100%)=∫S(a, λ)·σ(Y toner, λ, 100%)dλ  (43)B(a, Y ink, 100%)=∫S(a, λ)·σ(Y ink, λ, 100%)dλ  (44)The spectral sensitivity S (a, λ) is assumed to be a representativevalue of the scanner section 300 to be used and Y toner σ (Y toner, λ)and Y ink spectral reflection factor σ (Y ink, λ) are measured by aspectrophotometric colorimetry device. Consequently, it is possible tocalculate B (a, Y toner) and B (a, Y ink) can be calculated.

In predicting, based on the read value B (Y ink) of the blue signalobtained by reading the yellow patch of the printing ink on the linkagecolor correction chart HC, the read value B (Y toner) at the time when Ytoner is read as a read value for Y toner at the execution of the ACC,the following Equation 45 is used as a correction coefficient k(Yellow).B(Y toner)=k(Yellow)×B(Y ink)  (45)where k (Yellow)=B(a, Y toner, 100%)/B(a, Y ink, 100%).

Although the yellow toner is explained above, concerning other colorpatches, a Y toner area ratio or a toner deposition amount per a unitarea mg/cm2, at which the spectral reflection factor of the yellow tonerand the reflectivity of a color patch of a printing ink to be calculatedare substantially equal in an area in which the blue spectralsensitivity of the CCD 312 is not 0, is used.

For example, concerning a patch for which the read values of thespectral reflection factor characteristic (i) of blue green ink shown inFIG. 41 and the yellow toner spectral reflection factor (c) and the bluesignal at an area ratio of 50% are lower than the read value of yellowtoner (ink) (e.g., Black, Green), the calculation of the correctioncoefficient is not performed and 1 is used as the coefficient. It ispossible to represent the correction coefficient k calculated in thisway as shown in FIG. 39.

A method of creating an ACC pattern read value correction conversiontable is explained based on a quaternary chart of an ACC pattern readvalue correction table shown in FIG. 42.

A first quadrant (1) in FIG. 42 represents a conversion table forcorrection of a required ACC pattern read value in which a horizontalaxis represents a CCD pattern read value and a vertical axis representsa value after conversion. In a fourth quadrant (IV), a vertical axisrepresents a read value after correction with a correction coefficient kby chromatic and achromatic patches and a graph shows a target value (areference value) for the purpose of obtaining a conversion table for acorrection of ACC pattern read value based on read values of chromaticand achromatic patches. In a third quadrant (III), a horizontal axisrepresents a reference value of read values of chromatic and achromaticpatches and a graph represents a value obtained by correcting a readvalue, which is obtained by reading the chromatic and achromaticpatches, with a scanner with the correction coefficient k. A secondquadrant (II) represents no conversion (through).

According to the characteristics shown in FIG. 42, based on results “a”and “a′” of the read value of the third quadrant (III), a conversiontable (correction table) D [ii] (ii=0, 1, 2, . . . , 255) for thecorrection of the ACC pattern read value required by the first quadrant(1) b, b′ is created, respectively.

A target value of a read value shown in the fourth quadrant (IV) in FIG.42 is created for the respective toners of Y, M, C, and K read by theACC pattern. In this way, it is possible to improve adjustment accuracyof the ACC.

FIG. 43 is a schematic of an example of values obtained by reading colorpatches extracted for the correction of cyan toner with a scannerserving as a reference. In reading cyan toner, since sensitivity of ared signal is high, the red signal is used. Thus, a correction table forcyan toner reading at the time of ACC execution is created by using redsignals of chromatic and achromatic patches of 1.white, 2. yellow, 3.red (or 4. magenta), 5. color 1 between magenta and blue, 6. color 2between magenta and blue, 7. blue, 8. cyan, 10. gray, and 11. black thatoutput different red signal values from a plurality of chromatic colorpatches having different tints.

Consequently, it is possible to prevent fluctuation in reading imagesignals due to the difference in the scanner sections 300 and improvethe adjustment accuracy of the ACC. Therefore, it is possible to furtherimprove an image quality.

Moreover, a gradation conversion table set for the image processingprinter gamma conversion circuit 713 when a gradation pattern is read isgenerated using an image signal having a common one component in imagesignals obtained by reading a plurality of different color patches ofthe linkage color correction chart HC by the scanner section 300. Thus,it is possible to improve adjustment accuracy of a gradation conversiontable and improve, even when a linkage output is performed, an imagequality by using, among the R, G, and B image signals obtained byreading different color patches of the linkage color correction chartHC, the reading image signal of the scanner section 300 corresponding toa complementary color signal of Y, M, and C toners.

Furthermore, when a cyan reading scanner gamma conversion table at theexecution of the ACC is created, the linkage color correction chart HCis created by printing ink. This causes a difference of a spectralreflection factor from that of toner. FIG. 43 shows an example ofcorrection coefficients for the correction for red.

In this way, it is possible to create a further superior scanner gammaconversion table as an image signal conversion table for the ACC andfurther improve an image quality by correcting a difference between thespectral reflection factor characteristic of the printing ink of thelinkage color correction chart HC and the toner spectral reflectionfactor characteristic of the printer section 100 that records andoutputs a gradation pattern.

An operation screen for selecting an ACC function for imageconcentration (gradation characteristic) is described.

When the ACC menu is called up in the liquid crystal screen 511 of theoperation section 500 shown in FIG. 4, an automatic gradation adjustmentscreen shown in FIG. 44 is displayed. When [execution] of automaticgradation correction for copy use or for printer use is selected in thisautomatic gradation adjustment screen, an automatic gradation correctionstart screen shown in FIG. 45 is displayed on the liquid crystal screen511. In this case, when “copy use” is selected in the automaticgradation adjustment screen of FIG. 44, a gradation correction tableused for copy use is created and, when “printer use” is selected, agradation correction table for printer use is created based on referencedata.

In the automatic gradation adjustment screen in FIG. 44, a “return tooriginal” key is displayed such that, when a result of performing imageformation by the Y, M, C, and K gradation correction table after changeis not desirable, it is possible to select the Y, M, C, and K gradationcorrection table before the processing.

When “automatic gradation correction setting” is selected, keys for theselection of “background correction”, “high concentration partcorrection”, “RGB ratio correction”, “execution” or “non-execution” isdisplayed on in the automatic gradation adjustment screen of FIG. 44. Inthe “automatic gradation correction setting” menu, it is possible toselect “automatic gradation correction setting” and “setting ofdetection of uneven light intensity”. Note that these selections are notalways required and “executed” may be always set.

The color copying apparatus 1 creates the scanner gamma conversion tablefor the respective R, G, and B reading components used in the copy froman achromatic patch as described above. On the other hand, the colorcopying apparatus 1 corrects the read values of the respective Y, M, C,and K gradation patterns obtained by reading the adjustment patternoutput at the time of execution of ACC from the chromatic patch and theachromatic patch. Thus, the former processing uses the three conversiontables for R, G, and B while the latter processing uses the fourconversion tables for Y, M; C, and K.

Operations of the ACC of the image concentration (gradationcharacteristic) are explained based on a flowchart shown in FIG. 46.

When “execution” of the automatic gradation correction for copy use orprinter use is selected in the automatic gradation adjustment screenshown in FIG. 44, the automatic gradation correction start screen shownin FIG. 45 is displayed on the liquid crystal screen 511. When the“print start” key at the start of this automatic gradation correction isdepressed, a plurality of concentration gradation patterns shown in FIG.47 that correspond to the respective colors of Y, M, C, and K andrespective image quality modes of characters and photographs are formedon the transfer paper (the transfer material) P (step S101).

This concentration gradation pattern is stored and set 00h, 10h, 20h,30h, 40h, 50h, 60h, 70h, 90h, BOh, EOh, FFh

The color copying apparatus 1 causes the development units 107K to 107Cto develop latent images of the detection patterns of the photosensitiveelement drums 104K to 104C into visual images (step S303). The colorcopying apparatus 1 acquires a detection output VPi (i=1, 2, . . . , np)of toner images on the photosensitive element drums 104K to 104C withthe optical sensors 616K to 616C provided at the downstream in therotation direction of the photosensitive element drums 104K to 104C(step S304).

The color copying apparatus 1 estimates a development characteristicbased on this surface potential VSi of the photosensitive element drums104K to 104C obtained by the potential sensor 617 and the detectionoutput VPi of the toner image on the photosensitive element drums 104Kto 104 c obtained by the optical sensors 616K to 616C (step S305) andcreates a gradation conversion table (step S306).

Thus, first, a method of correcting outputs of the optical sensors 616Kto 616C and image signals is performed as shown in FIG. 55. In a graph(a) in FIG. 55, a vertical axis represents a laser output or an imageoutput signal and a horizontal axis represents outputs of the opticalsensors 616K to 616C. After the np concentration gradation patternlatent images are formed on the photosensitive in the ROM 716 of the IPU612 in advance and is written with hexadecimal values of sixteenpatterns of 00h, 11h, 22h, . . . , EEh, and FFh. Although patches for 5tones except a background section are displayed in FIG. 47, it ispossible to select an arbitrary value out of 8-bit signals of 00h toFFh. The concentration gradation patterns include a character mode and aphotograph mode. In the character mode, dither processing (e.g., patternprocessing) is not performed and a pattern with 256 tones for one dot isformed. In the photograph mode, the dither processing (which will bedescribed later) is performed.

When the color copying apparatus 1 outputs a pattern to the transferpaper (transfer material) P, the liquid crystal screen 511 displays amessage as shown in FIG. 48 to request a user to place the transferpaper (the transfer material) P with the concentration gradation patternrecorded and output thereon on the contact glass 3 serving as anoriginal stand. When the transfer paper with the concentration gradationpattern formed thereon is placed on the contact glass 3 according to theinstruction on this screen (step S102), it is checked whether “readingstart” or “cancel” is selected on the screen in FIG. 48 (step S103).When “cancel” is selected, the processing is completed.

When “reading start” is selected at step S103, the color copyingapparatus 1 causes the scanner section 300 to subject the transfer paperwith the concentration gradation pattern formed thereon to main scanningand sub-scanning to read the RGB data of the Y, M, C, and Kconcentration patterns (step S104). In this case, the scanner section300 reads data of a pattern part of the transfer paper with theconcentration gradation pattern formed thereon and data of thebackground section of the transfer paper.

The color copying apparatus 1 judges whether the data of the patternpart of the transfer paper is correctly read (step S105). When thepattern part of the transfer paper is not correctly read, the colorcopying apparatus 1 checks whether the data is not correctly read forthe second time (step S106). When the data is not correctly read for thefirst time, the color copying apparatus 1 causes the liquid crystalscreen 511 to display the screen in FIG. 48. When the reading isinstructed, the processing returns to step S104 to perform theprocessing as described above (steps S104 and S106). When the data isnot correctly read for the second time at step S106, the processing iscompleted.

When the data of the pattern part of the transfer paper is correctlyread at step S105, the color copying apparatus 1 converts and correctsthe respective read values of the ACC patterns for the respective colorsof Y, M, C, and K based on the ACC pattern read value correction tableD[ii] (ii=0, 1, 2, . . . , 255) (step S107) to determine, based on aresult of the selection in the automatic gradation adjustment screen ofFIG. 44, “execution” or “non-execution” of the background correctionprocessing using the background data (step S108).

When “execution” of the background correction processing is selected atstep S108, the color copying apparatus 1 applies the background datacorrection processing to the read data (step S109) and judges“execution” or “non-execution” of the correction of a high imageconcentration part of the reference data based on the selection resultin the automatic gradation adjustment screen of FIG. 44 (step S110).

When “execution” of the correction of the high image concentration partof the reference data is selected at step S110, the color copyingapparatus 1 applies the correction processing of the high imageconcentration part to the reference data (step S111) to create andselect the YMCK gradation correction table (step S112). When thecorrection of the reference data is not performed at step S110, thecolor copying apparatus 1 creates and selects the YMCK gradationcorrection table without correcting the reference data (step S112).

When the color copying apparatus 1 creates and selects the YMCKgradation correction table, the color copying apparatus 1 checks whetherthe processing is performed for the respective colors of Y, M, C, and K(step S113) and, when the processing is not performed for the respectivecolors of Y, M, C, and K, returns to step S105 to execute the processingfor the respective colors of Y, M, C, and K (steps S105 to S113).

When the processing for the respective colors of Y, M, C, and K isperformed at step S113, the color copying apparatus 1 checks whether theprocessing is completed for the respective image quality modes ofphotographs and characters (step S114). When the processing is notcompleted, the color copying apparatus 1 returns to step S105 to performthe processing as described above (steps S105 to S114). When theprocessing for the respective image quality modes of photographs andcharacters is completed at step S114, the color copying apparatus 1 endsthe processing.

During the processing, the color copying apparatus 1 causes the liquidcrystal screen 511 to display a screen indicating that the automaticgradation correction is being executed as shown in FIG. 49. When aresult of the image formation according to the YMCK gradation correctiontable after the processing is not desirable, the automatic gradationadjustment screen in FIG. 44 displays the “return to an original state”key such that it is possible to select the YMCK gradation correctiontable before the processing.

The background correction processing is described. The backgroundcorrection processing has two objectives. The first objective is tocorrect a white level of transfer paper used in the ACC. The reason whythe background correction processing is performed is that, even when asingle image is formed by a single machine, a value read by the scannersection 300 is different depending on the white level of the transferpaper. When the correction is not performed, there are disadvantages,for example, the white level is low. In addition, when a recycled paperor the like is used for the ACC, a yellow gradation correction table forthe recycled paper is created. Thus, correction is performed to reducethe yellow component because the recycled paper generally includes alarge quantity of yellow component. However, when copying is performedusing, for example, art paper having a high white level, since an imagehas less yellow component, desirable color reproducibility may not beobtained.

Another reason for performing the background correction processing isthat, when transfer paper (paper thickness) used for the ACC is thin,for example, a pressure plate for pressing the transfer paper is seenthrough the paper and is read by the scanner section 300. For example,when the ADF 400 is attached instead of the pressure plate, the belt 402is used to convey the original G. However, this conveyor belt 402 has alow white level due to its rubber-base material and has a slightly graycolor. Thus, an image signal is read as an image signal that is entirelyhigh concentration in appearance. The belt 402 is created to be thinneraccordingly when the YMCK gradation correction table is created.However, when transfer paper having large thickness and low translucencyis used for the ACC, an image having entirely low concentration isreproduced. Therefore, a desirable image is not always obtained.

In order to prevent the defect as described above, a reading imagesignal of a pattern part is corrected based on a reading image signal ofa paper background section and an image signal of the paper backgroundsection.

However, there are also advantages when the correction is not performed.When transfer paper including a large quantity of yellow component(e.g., recycled paper) is always used, color reproducibility is betterwith respect to a color containing a yellow component. In addition, whenonly transfer paper having small thickness is used, a gradationcorrection table is created to be suitable for the thin paper.

Thus, in the color copying apparatus 1, with the operation of the key ofthe operation section 500, it is possible to turn ON or OFF thecorrection of the background section deepening on a status of use of thecolor copying apparatus 1, preference of the user, or the like.

Operations and processing of the automatic gradation correction aredescribed. Read Value obtained by reading, with the scanner section 300,a gradation pattern (see FIG. 47) formed on transfer paper includingwriting values LD [i] (i=0, 1, . . . , 9) are set to bev[t][i]=≡(r[t][i],g[t][i],t[b][i]) (t=Y,M,C,or,K,i=0, 1, . . . , 9) in avector format.

Note that, instead of (r, g, b), the read values also may be representedby brightness, saturation, hue angle (L*, c*, h*), or brightness,redness, blueness (L*, a*, b*), and the like.

Read values of white stored in the ROM 716 or the RAM 717 is advance areset to be (r[W], g[W], b[W]).

A method of generating a gradation conversion table (LUT) in the imageprocessing printer gamma conversion circuit 713 at the time of executionof the ACC is described.

In the read values of the gradation pattern v[t][i]=(r[t][i], g[t][i],b[t][i]), image signals of the respective complementary colors of Y, M,and C toners are b[t][i], g[t][i], and r[t][i]. Thus, only image signalsof the respective complementary colors are used. For simplicity ofexplanation, the read values are represented using a[t][i] (i=0, 1, 2, .. . , 9; t=C, M, Y, or, K). Processing is simple when a gradationconversion table is created.

Note that black toner provides a sufficient accuracy when any one of theR, G, and B image signals is used. A G (green) component is used here.

Reference data is given by a combination of a read value v0[t][i] of thescanner section 300 v0[t][i]=(r0[t][i], g0[t][i], b0[t][i]) and laserwriting values LD[i](i=1, 2, . . . , m) corresponding thereto.Similarly, only the Y, M, and C complementary color image signals areused to represent the data as, for simple illustration,A[t][n[i]](0≦n[i]≦255; i=1, 2, . . . , m; t=Y, M, C, or, K). “m” is thenumber of reference data.

A YMCK gradation conversion table is obtained by comparing the a[LD]with reference data A[n] stored in the ROM 716.

Here, “n” is an input value to the YMCK gradation conversion table andthe reference data A[n] is a target value of the reading image signalobtained by reading, with the scanner section 300, a YMC toner patternoutput with the laser writing value LD[i] after the input value n issubjected to the YMCK gradation conversion. The reference data consistsof two values of the reference value A[n] for which the correction isperformed depending on the image concentration that can be output by theprinter and the reference value A[n] for which the correction is notperformed. The color copying apparatus 1 determines whether thecorrection is performed based on data for determination stored in theROM 716 or the RAM 717 is advance.

The color copying apparatus 1 calculates LD corresponding to A[n] basedon a[LD] to obtain a laser output value LD[n] corresponding to an inputvalue n to the YMCK gradation conversion table.

By calculating this laser output value LD[n] with respect to the inputvalue i=0, 1, . . . , 255 (in the case of 8-bit signal), it is possibleto obtain a gradation conversion table.

Instead of applying the processing to all values corresponding to theinput values n=00h, 01h, . . . , FFh (hexadecimal digit) to the YMCKgradation conversion table, discontinuous values such as ni=0, 11h, 22h,. . . , FFh is subjected to the processing and points other than thevalues are subjected to an interpolation by the spline function or thelike or the closest table passing the combination of (0, LD[0]), (11h,LD[11h]), (22h, LD[22h]), . . . , (FFh, LD[FFh]) calculated in theprocessing is selected out of the YMCK γ correction tables stored in theROM 716 in advance.

The above processing is explained with reference to FIG. 50. In a firstquadrant (a) in FIG. 50, a horizontal axis represents an input value nto the YMCK gradation conversion table while a vertical axis representsa read value (after the processing) by the scanner section 300 thatrepresents the reference data A[i]. The read values (after theprocessing) by the scanner section 300 are values obtained by subjectingvalues obtained by reading gradation patterns with the scanner section300 to the RGB gamma conversion (not performed here), averagingprocessing for read data at a few positions in the gradation pattern,and addition processing. In order to improve calculation accuracy,12-bit data signal is used for the processing.

In FIG. 50, both of a horizontal axis and a vertical axis of a secondquadrant (b) represent read values (after processing) of the scannersection 300.

In FIG. 50, a vertical axis of a third quadrant (c) represents a laserlight (LD) writing value. Data a[LD], which is a writing value of thelaser light, represents a characteristic of the printer section 100.Laser light (LD) writing values of a pattern actually formed are sixteenpoints of 00h (background), 11h, 22h, . . . , EEh, FFh consisting ofdiscontinuous values. However, spaces between detection points areinterpolated to be treated as a continuous graph.

In FIG. 50, a graph (d) of a fourth quadrant is a YMCK gradationconversion table LD[i] and is provided for the purpose of obtaining thisYMCK gradation conversion table.

In a graph (f), a vertical axis and a horizontal axis are the same asthe vertical axis and the horizontal axis of the graph (d). When agradation pattern for detection is formed, a YMCK gradation conversiontable (g) shown in the graph (f) is used.

A horizontal axis of the graph (e) is the same as the horizontal axis ofthe third quadrant (c) and represents linear conversion for conveniencerepresenting a relation between a laser light (LD) writing value at thetime when a gradation pattern is created and a read value (afterprocessing) of a gradation pattern by the scanner section 300.

In FIG. 50, a reference data A[n] is obtained with respect to the inputvalue n and a laser light (LD) output LD[n]to obtain the A[n] is foundalong an arrow (1) in FIG. 50 using the gradation pattern read valuea[LD].

FIG. 51 illustrates an example of a Green data conversion table. A parthaving a read value with a large quantity of reflected light from a1000H-side original (light part) uses a read value of a Magentacalibration pattern 1 while a part having a small amount of reflectedlight from an OH-side original (dark part) uses a Black read value forthe generation.

The ACC calculation procedure is explained with reference to a flowchartin FIG. 52. In FIG. 52, first, ACC gradation conversion table creationprocessing causes the color copying apparatus 1 to determine an inputvalue (e.g., n[i]=11(h)xi(i=0, 1, . . . , imax=15)) required to obtain aYMCK 7 correction table (a gradation conversion table) (step S201).

Compared with the graph at the time when the RGB gamma conversion isperformed, the same printer characteristic graph is obtained but an RGBgamma conversion table of a second quadrant has a differentcharacteristic. Therefore, reference data of a first quadrant must bechanged. However, a characteristic of the YMCK gradation conversiontable LD[h], which is a final result, is the same.

As described above, the reference data is changed depending on whetherthe processing by the RGB gamma conversion table is performed. Theexample of the RGB gamma conversion table used in this embodiment isdescribed above.

The color copying apparatus 1 corrects the reference data A[n] accordingto the image concentration that can be output by the printer section 100(step S202).

A laser light writing value for obtaining maximum image concentration,which can be created by the printer section 100, is set as FFh(hexadecimal indication) and a read value m [FFh] of a gradation patternat this point is set as mmax. Reference data from a low imageconcentration side to an intermediate image concentration side for whichcorrection is not performed is set as A[i](i=0, 1, . . . , i1),reference data on a high image concentration side for which correctionis not performed is set as A[i](i=i2+1, imax−1)(i1≦i2, i2≦imax−1), andreference data for which correction is performed is set as A[i](i=i1+1,. . . , 12).

In the following explanation, assuming an image signal proportional toan original reflectivity for which the RGB gamma conversion is notperformed, a specific calculation method is explained. Among referencedata for which correction is not performed, reference data A[i2+1] of ahigh image concentration part that has lowest image concentration and areference data A[i1] of a low image concentration part that has lowestimage concentration are used to calculate the difference Δref of thedata with the following Equation 46.Δref=A[i1]−A[i2+1]  (46)where in the case of reflectivity linear or brightness linear data forwhich the RGB gamma conversion serving as inversion processing is notperformed, Δref>0.

On the other hand, based on a read value mmax of a gradation patternthat can be created by the printer section 100, for which maximum imageconcentration is obtained, a difference Δdet is similarly calculated bythe following Equation 47.Δdet=A[i1]−mmax  (47)

Reference data A[i](i=i1+1, . . . , i2) subjected to the correction ofthe high concentration part is calculated by

the following Equation 48.A[i]=A[i1]+(A[i]−A[i1])×(Δdet/Δref)  (48)where i=i1+1, i1+2, . . . , i2−1, i2.

The color copying apparatus 1 calculates a reading image signal m[i] ofthe scanner section 300 corresponding to n[i] based on the referencedata A[n] (step S203).

Note that, to calculate this reading image signal m[i], actually,reference data A[n[j]] corresponding to discontinuous n[j] (0≦n[j]≦255,j=0, 1, . . . , jmax, n[j]≦n[k]for j≦k) is calculated as follows.j(0≦j≦jmax) with n[j]≦n[i]<n[j+1]

Note that, in the case of a 8-bit image signal, calculation issimplified if reference data is calculated as n[0]=0, n[jmax]=255,n[jmax+1], A[jmax+1]=A[jmax].

Accuracy of the γ correction table obtained finally is higher when aninterval of reference data n[j] is made narrow as much as possible.

The color copying apparatus 1 corrects the ACC pattern read value a[LD]to the writing value LD with the correction table D[ii](ii=0, 1, 2, . .. , 255) indicated as “b” or “b” in FIG. 42 as follow (step S204).a1[LD]=D[a[LD]]a1[LD] is represented as a[LD] below.

Based on “j” calculated in this way, m[i] is calculated by the followingEquation 49.m[i]=A[j]+(A[j+1]−A[i])*(n[i]−n[j])/(n[j+1]−n[j])  (49)

Note that, although interpolation is performed by a primary expressionin Equation 48, the interpolation may be performed by a higher orderfunction, a spline function, or the like. In this case, m[i] is given bythe followingm[i]=f(n[i])  (50)Where

${f(x)} = {\sum\limits_{i = 0}^{k}{bixi}}$in the case of a k-th order function.

When the color copying apparatus 1 calculates m[i], the color copyingapparatus 1 calculates a writing value LD[i] of a laser beam (LD) forobtaining m[i] in the same procedure (step S205). When image signal datanot subjected to RGB gamma conversion is processed, a[LD] becomessmaller as a value of the laser light (LD) increases as described below.

For LD[k]<LD[k+1], a[LD[k]]≧a[LD[k+1]]

Values during the pattern formation are ten values of LD[k]=00h, 11h,22h, . . . , 66h, 88h, AAh, FFh, (k=0, 1, . . . , 9). This is because,with image concentration with a small toner deposition amount, since achange in a read value of the scanner section 300 with respect to thetoner deposition amount is large, an interval of a writing value LD[k]of a pattern is set dense. With image concentration with a larger tonerdeposition amount, since a change in a read value of the scanner section300 with respect to a toner deposition amount is small, an interval isincreased for reading.

Consequently, there are advantages compared with the time when thenumber of patterns is increased in such a manner as LD[k]=00h, 11h, 22h,. . . , EEh, FFh (total of sixteen points). For example, tonerconsumption is controlled, a change with respect to an LD writing valueis small in a high image concentration area, and a reduced intervalbetween LD writing values is not always effective for an improvedaccuracy because of an influence of uneven potential on thephotosensitive element drums 104K to 104C, uneven deposition of toner,uneven fixing, or uneven potential. Thus, a pattern is formed with theLD writing value as described above.

Then, LD[i] is set as follows with respect to LD[k] for whicha[LD[k]]≧m[i]>a[LD[k+l]] is obtained.LD[i]=LD[k]+(LD[k+1]−LD[k])*(m[i]−a[LD[k]])/(a[LD[k+1]]−a[LD[k]])

When 0≦k≦kmax(kmax>0), if a[LD[kmax]]>m[i], LD[i] is estimated byperforming extrapolation with a primary expression (when the targetvalue calculated based on the reference data has a high imageconcentration) in the manner describe below.LD[i]=LD[k]+(LD[kmax]−LD[kmax−1])*(m[i]−a[LD[kmax−1]])/(a[LD[kmax]]−a[LD[kmax−1]])

Consequently, it is possible to obtain a set of an input value n[i] tothe YMCK γ correction table and an output value LD[i] (n[i], LD[i])(i=0, 1, . . . , 15).

Note that, other than the extrapolation with a primary expressiondescribed above, extrapolation may be performed by a method usinglogarithm or the like.

Based on the calculated (n[i], LD[I]) (i=0, 1, . . . , 15), the splinefunction or the like is used to perform an interpolation or a γcorrection table stored in the ROM 716 is selected to obtain a gradationconversion table (step S206).

The color copying apparatus 1 detects, to prevent background pollution(“fog”) and to secure concentration, a development characteristic (atoner deposition amount characteristic with respect to developmentpotential) as shown in FIG. 53.

As shown in FIG. 53, the color copying apparatus 1 forms np detectionpattern (a concentration gradation pattern) latent images on thephotosensitive element drums 104K to 104C (step S301) and acquires adetection output of a potential sensor (step S302).

As shown in FIG. 54, the color copying apparatus 1 forms np (e.g.,np=12) detection patterns (concentration gradation patterns) on thephotosensitive element drums 104K to 104C. The color copying apparatus 1reads a surface potential Vsi (i=1, 2, . . . , np) of the photosensitiveelement drums 104K to 104C with a potential sensor 617 that detects asurface potential. A laser output used for the formation of detectionpatterns has, for example, image signal values (hexadecimal indication)described below. element drums 104K to 104C, the latent images aredeveloped and an amount of reflected light of the toner images isdetected by the optical sensors 616K to 616C to obtain the graph.

In a graph (b) in FIG. 55, a vertical axis represents laser outputs asin the case of the graph (a) and a horizontal axis represents surfacepotentials of the photosensitive element drums 104K to 104C to representlight attenuation characteristics of the photosensitive element drums104K to 104C. As in the case of the graph (a), this graph (b) isobtained by measuring, with the potential sensor 617, surface potentialswhen the np concentration gradation pattern latent images are formed onthe photosensitive element drums 104K to 104C.

A graph (c) in FIG. 55 represents a gradation conversion table used forthe image formation by the printer section 100. A horizontal axisrepresents an image input signal (e.g., an amount proportional toconcentration of an original image) and a vertical axis represents animage signal (an image output signal) after a laser output of an imageinput signal is converted according to the gradation conversion table.The image input signal has a 8-bit (256 values) resolution and a laserwriting light amount also has the 8 (to 10) bit resolution between aminimum value and a maximum value of the laser. The graph (a) in FIG. 55represents a relation between a laser output used for the detection andan image input signal.

In a graph in FIG. 55, a vertical axis represents toner depositionamounts on the photosensitive element drums 104K to 104C while ahorizontal axis represents outputs of the optical sensors 616K to 616Cto represent output characteristics of the optical sensors 616K to 616C.The output characteristics of the optical sensors 616K to 616C in thegraph (d) are different depending on a type of the optical sensors 616Kto 616C to be used, an attachment angle, a distance from thephotosensitive element drums 104K to 104C, and the like. However, theoutput characteristics of the optical sensors 616K to 616C are known inadvance and are almost fixed.

In a graph (e) of FIG. 55, a vertical axis represents toner depositionamounts while a horizontal axis represents surface potentials of thephotosensitive element drums 104K to 104C to represent a relationbetween surface potentials of the photosensitive element drums 104K to104C and deposition amounts of toner on the photosensitive element drums104K to 104C (i.e., development characteristics). In the graph (e) inFIG. 55, “h” represents a DC component of a development bias.

A graph (f) in FIG. 55 represents a relation between an image inputsignal and an amount of toner deposited on the photosensitive elementdrums 104K to 104C.

Using the relation in the graph (d) in FIG. 55, an output VPi of theoptical sensors 616K to 616C is converted into toner deposition amountson the photosensitive element drums 104K to 104C (M/A)i[mg/cm2](i=1, 2,. . . , np). For example, reflected light of toner images formed on thephotosensitive element drums 104K to 104C is detected by the opticalsensors 616K to 616C and a result of the detection is sent as adetection signal to the CPU 715. The CPU 715 calculates, based on thefollowing Equation 51, a deposition amount m1 [g/cm2] per a unit area oftoner deposited on a reference pattern based on VSP and VSG as anoptical sensor output and a background section output based on a tonerdeposition amount in a reference pattern part, respectively.m1=−ln(VSP/VSG)/β  (51)where β is a constant determined by the optical sensors 616K to 616C andtoner and, in the case of black toner, β=−6.0×10³ [cm2/g]. Note thatoutputs are converted in the same manner for yellow, cyan, and magenta.

Although a deposition amount per a unit area m1 [g/cm2] of tonerdeposited to a reference pattern is calculated in the above explanation,outputs may be converted to calculate the deposition amount with alookup table created in advance.

As described above, a relation between the surface potential VSi on thephotosensitive element drums 104K to 104C and the toner depositionamount (M/A)i on the photosensitive element drum 104K to 104C isobtained and a development characteristic j in the graph (e) of FIG. 55is obtained.

However, as shown in a graph (d) of FIG. 55, outputs of the opticalsensors 616K to 616C indicate a fixed value Vpmin in the case of a tonerdeposition amount ((M/A)≧(M/A)C) higher than a certain toner depositionamount (M/A)C. On the other hand, with respect to an image signal equalto or higher than an “n” image signal in the graph (c) in FIG. 55,surface potentials on the photosensitive element drums 104K to 104Cactually decrease as shown in the graph (b). Regardless of a change inthe toner deposition amount, a toner deposition amount (M/A) on thephotosensitive element drums 104K to 104C always takes a fixed value(M/A)C. Thus, in the graph (e), a development characteristic obtainedbased on the detection result is as indicated by “j” even when an actualdevelopment characteristic is as indicated by the graph c. This causes adifference between the actual value C and the detected value j.

In order to compensate for the difference between the actual developmentcharacteristic and the development characteristic calculated based onthe detection value, correction described below is performed.

When the detection value VPi of the optical sensors 616K to 616C to theimage signal i is equal to or higher than the predetermined value VPc,the detection value VPi is converted into a toner deposition amount onthe photosensitive element drums 104K to 104C or (M/A)I nearlyproportional to the toner deposition amount. Based on these values, arelational expression of the output value VSi of the potential sensor617 and the (M/A)I are calculated, for example, as indicated by thefollowing Equation 52 using a primary expression(M/A)i=a×VSi+b  (52)where VPi≧vPc.

Alternatively, a DC component of a development bias is assumed to be Vdcto obtain a relational expression as indicated by the following Equation53.(M/A)i=a×(VSi−Vdc)+b  (53)where VPi≧VPc.

“a” and “b” are coefficients determined by a method such as aleast-squares method based on the values of VSi and (M/A)I.

Assuming that a toner deposition amount on the photosensitive elementdrums 104K to 104C at the time when output values of the optical sensors616K to 616C are VPc is (M/A)C, a range of the deposition amountsatisfying (M/A)i≦(M/A)C is the same. This may increase a deviationbecause of a linear relation with the surface potential. In order toprevent such a case, the coefficients “a” and “b” of the Equation 52 aredetermined with respect to the detection result of the toner depositionamount on the photosensitive element drums 104K to 104C that satisfies(M/A)min≦(M/A)≦(M/A)C.

Although the toner deposition amount is used in the above explanation, adetected output of the optical sensors 616K to 616C corresponding to(M/A)min may be assumed as VPmax to determine the coefficients “a” and“b” of Equation (14) based on a toner deposition area the tonerdeposition area satisfying the following Equation 54.VPc≦VP≦VPmax  (54)

As described above, a gradation conversion table determined for theimage processing printer gamma conversion circuit 713 for a gradationpattern reading is generated by the following procedure. First, amongimage signals obtained by reading, with the scanner section 300, aplurality of different colors of patches of the linkage color correctionchart HC with respect to an image signal having one common component,read patches are used to calculate different predetermined coefficients“a” and “b”. A table is generated according to an image signalcalculated by the calculation. With this table, it is possible tocorrect a difference between a characteristic of a spectral reflectionfactor of printing ink of the linkage color correction chart HC and acharacteristic of a spectral reflection factor of toner of the printersection 100 that records and outputs a gradation pattern to create afurther superior gradation conversion table for the ACC. Therefore, itis possible to further improve an image quality.

As described above, according to this embodiment, based on the readvalues in the linkage color correction chart HC that consists of aplurality of achromatic patches and a plurality of chromatic patcheshaving different concentrations and reference values in the linkagecolor correction chart HC, a masking coefficient according to each huearea is calculated and an image signal after the gradation conversion ofthe input image signal from the scanner section 300 is correctedaccording to the masking coefficient. Consequently, at the execution ofthe linkage output function, it is possible to reduce deterioration withtime and use of a scanner optical system, a machine difference of ascanner due to fluctuation in spectral transmission rate and spectralsensitivity among machines (e.g., CCD, infrared-ray cut filter), improvethe printer adjustment accuracy, and reduce fluctuation in adjustment.

Moreover, it is possible to highly accurately correct, even whenconcentration or tint in the linkage color correction chart HC fluctuatein the market, the fluctuation by using a deviation amount between aread value and a reference value without using an absolute value of aread value.

Furthermore, according to this embodiment, a masking coefficientaccording to each hue area for correcting an image signal aftergradation conversion of an input image signal from the scanner section300 is calculated by reading, with the scanner section 300, the linkagecolor correction chart HC consisting of a plurality of achromaticpatches and a plurality of chromatic patches having differentconcentrations to compare the linkage color correction chart HC with areference value set in advance of the linkage color correction chart HC.Consequently, it is possible to reduce, at the execution of the linkageoutput function, deterioration with time and use of a scanner opticalsystem, reduce the a machine difference of a scanner due to fluctuationin spectral transmission rate and spectral sensitivity among machines(e.g., CCD, infrared-ray cut filter), improve the printer adjustmentaccuracy, and reduce fluctuation in adjustment.

A second embodiment of the present invention is explained with referenceto FIGS. 56 to 58. Note that components same as those in the firstembodiment are denoted by the same reference numerals and explanationsof the components are omitted.

FIG. 56 is a circuit block diagram of the IPU 612 and the printersection 100 in the color copying apparatus 1 according to thisembodiment. In FIG. 56, reference numeral 300 denotes a scanner; 1401, ashading correction circuit; 1402, a scanner gamma conversion circuit;1403, an image memory; 1404, an image separation circuit; 1405, a MTFfilter; 1406, a color conversion UCR processing circuit; 1407, anenlargement/reduction circuit; 1408, image processing (create) circuit;1409, an image processing printer gamma conversion circuit; 1410, agradation processing circuit; 1411, an interface I/F selector; 1412, animage formation section printer γ (hereinafter referred to as PROCON γ)conversion circuit; 724, a printer engine; 1414, a ROM; 1415, a CPU;1416, a RAM; 1417, a system controller; and 1421 and 1422, patterngeneration circuits.

With reference to FIG. 56, operations of the IPU 612 are described. Anoriginal to be copied is subjected to color separation by the colorscanner 300 to be separated into R, G, and B and is read with a 10-bitsignal as an example. The read image signal is corrected by the shadingcorrection circuit 1401 such that unevenness in the main scanningdirection is corrected and is output with an 8-bit signal.

The scanner gamma conversion circuit 1402 converts a reading signal fromthe scanner 300 from reflectivity data to brightness data. The imagememory 1403 stores the image signal after the scanner gamma conversion.The image separation circuit 1404 determines a character part and aphotograph part and determines a chromatic part and an achromatic part.

The MTF filter 1405 performs edge enhancement processing correspondingto an edge level of an image signal (adaptation edge enhancementprocessing) in addition to processing for changing a frequencycharacteristic of an image signal such as edge enhancement or smoothingfor providing a sharp image or a soft image suitable for the preferenceof a user. For example, the MTF filter 1405 applies so-called adaptationedge enhancement to the respective R, G, and B signals in which acharacter edge is subjected to an edge enhancement and a halftone dotimage is subjected to an edge enhancement. Details of the MTF filter1405 are the same as those of the MTF filter 707 explained in the firstembodiment with reference to FIG. 7. Thus, the details are not furtherexplained.

An embodiment corresponding to a first aspect of the present inventionis explained. In the present invention, to correct a difference ofspectral characteristics for respective CCDs, a linear maskingcoefficient is calculated as a new linear masking coefficient based on aread value of the scanner data calibration standard chart shown in FIG.26. A method for the calculation is explained below.

A value obtained by reading a point on a boundary surface not existingon an achromatic axis with a scanner CCD indicating, for example, astandard spectral characteristic is set as (Ri, Gi, Bi) (i=hue 1 to 4).When this point is read by another scanner, because of fluctuation inthe spectral characteristics of the scanner CCDs, this point is read as(Ri′, Gi′, Bi′) (i=hues 1 to 4) different from (Ri,Gi,Bi)(i=hues 1 to4). As a result, recording values of the development sections C, M, Y,and K are calculated as (Ci′, Mi′, Yi′, Ki′) (i=hues 1 to 4). It ispossible to represent Equation 33 as indicated by the following Equation55.

$\begin{matrix}{\begin{pmatrix}{Y\left( 1^{\prime} \right)} & {Y\left( 2^{\prime} \right)} & {Y\left( 3^{\prime} \right)} & {Y\left( 4^{\prime} \right)} \\{M\left( 1^{\prime} \right)} & {M\left( 2^{\prime} \right)} & {M\left( 3^{\prime} \right)} & {M\left( 4^{\prime} \right)} \\{C\left( 1^{\prime} \right)} & {C\left( 2^{\prime} \right)} & {C\left( 3^{\prime} \right)} & {C\left( 4^{\prime} \right)} \\{K\left( 1^{\prime} \right)} & {K\left( 2^{\prime} \right)} & {K\left( 3^{\prime} \right)} & {K\left( 4^{\prime} \right)}\end{pmatrix} = {\left( {\begin{matrix}{\;{{aYB}\left( {3^{\prime}4^{\prime}} \right)}} \\{\;{{aMB}\left( {3^{\prime}4^{\prime}} \right)}} \\{\;{{aCB}\left( {3^{\prime}4^{\prime}} \right)}} \\{\;{{aKB}\left( {3^{\prime}4^{\prime}} \right)}}\end{matrix}\begin{matrix}{{aYG}\left( {3^{\prime}4^{\prime}} \right)} & {{aYR}\left( {3^{\prime}4^{\prime}} \right)} & {{aY}\left( {3^{\prime}4^{\prime}} \right)} \\{{aMG}\left( {3^{\prime}4^{\prime}} \right)} & {{aMR}\left( {3^{\prime}4^{\prime}} \right)} & {{aM}\left( {3^{\prime}4^{\prime}} \right)} \\{{aCG}\left( {3^{\prime}4^{\prime}} \right)} & {{aCR}\left( {3^{\prime}4^{\prime}} \right)} & {{aC}\left( {3^{\prime}4^{\prime}} \right)} \\{{aKG}\left( {3^{\prime}4^{\prime}} \right)} & {{aKR}\left( {3^{\prime}4^{\prime}} \right)} & {{aK}\left( {3^{\prime}4^{\prime}} \right)}\end{matrix}} \right)\begin{pmatrix}{B\left( 1^{\prime} \right)} & {B\left( 2^{\prime} \right)} & {B\left( 3^{\prime} \right)} & {{B\left( 4^{\prime} \right)}\;} \\{G\left( 1^{\prime} \right)} & {G\left( 2^{\prime} \right)} & {G\left( 3^{\prime} \right)} & {G\left( 4^{\prime} \right)} \\{R\left( 1^{\prime} \right)} & {R\left( 2^{\prime} \right)} & {R\left( 3^{\prime} \right)} & {R\left( 4^{\prime} \right)} \\1 & 1 & 1 & 1\end{pmatrix}}} & (55)\end{matrix}$

Assuming that Equation 32 is equal to Equation 55 to make Y, M, C, and Koutputs after linear masking processing identical, the followingEquation is obtained.

$\begin{matrix}{\begin{pmatrix}{Y(1)} & {Y(2)} & {Y(3)} & {Y(4)} \\{M(1)} & {M(2)} & {M(3)} & {M(4)} \\{C(1)} & {C(2)} & {C(3)} & {C(4)} \\{K(1)} & {K(2)} & {K(3)} & {K(4)}\end{pmatrix} = {{\begin{pmatrix}{{aYB}\left( {3\mspace{14mu} 4} \right)} & {{aYG}\left( {3\mspace{14mu} 4} \right)} & {{aYR}\left( {3\mspace{14mu} 4} \right)} & {{aY}\left( {3\mspace{14mu} 4} \right)} \\{{aMB}\left( {3\mspace{14mu} 4} \right)} & {{aMG}\left( {3\mspace{14mu} 4} \right)} & {{aMR}\left( {3\mspace{14mu} 4} \right)} & {{aM}\left( {3\mspace{14mu} 4} \right)} \\{{aCB}\left( {3\mspace{14mu} 4} \right)} & {{aCG}\left( {3\mspace{14mu} 4} \right)} & {{aCR}\left( {3\mspace{14mu} 4} \right)} & {{aC}\left( {3\mspace{14mu} 4} \right)} \\{{aKB}\left( {3\mspace{14mu} 4} \right)} & {{aKG}\left( {3\mspace{14mu} 4} \right)} & {{aKR}\left( {3\mspace{14mu} 4} \right)} & {{aK}\left( {3\mspace{14mu} 4} \right)}\end{pmatrix}\begin{pmatrix}{B(1)} & {B(2)} & {B(3)} & {B(4)} \\{G(1)} & {G(2)} & {G(3)} & {G(4)} \\{R(1)} & {R(2)} & {R(3)} & {R(4)} \\1 & 1 & 1 & 1\end{pmatrix}} = {\begin{pmatrix}{{aYB}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aYG}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aYR}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aY}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} \\{{aMB}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aMG}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aMR}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aM}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} \\{{aCB}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aCG}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aCR}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aC}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} \\{{aKB}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aKG}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aKR}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aK}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)}\end{pmatrix}\begin{pmatrix}{B\left( 1^{\prime} \right)} & {B\left( 2^{\prime} \right)} & {B\left( 3^{\prime} \right)} & {B\left( 4^{\prime} \right)} \\{G\left( 1^{\prime} \right)} & {G\left( 2^{\prime} \right)} & {G\left( 3^{\prime} \right)} & {G\left( 4^{\prime} \right)} \\{R\left( 1^{\prime} \right)} & {R\left( 2^{\prime} \right)} & {R\left( 3^{\prime} \right)} & {R\left( 4^{\prime} \right)} \\1 & 1 & 1 & 1\end{pmatrix}}}} & {(56)\mspace{56mu}}\end{matrix}$According to Equation 56, to calculate a linear masking coefficient aPS(hues 3′ to 4′) (P=Y, M, C, K; S=R, G, B) of the hue areas 3′ and 4′,both sides are multiplied by an inverse matrix

$\begin{matrix}{B\left( 1^{\prime} \right)} & {B\left( 2^{\prime} \right)} & {B\left( 3^{\prime} \right)} & {B\left( 4^{\prime} \right)} \\{G\left( 1^{\prime} \right)} & {G\left( 2^{\prime} \right)} & {G\left( 3^{\prime} \right)} & {G\left( 4^{\prime} \right)} \\{R\left( 1^{\prime} \right)} & {R\left( 2^{\prime} \right)} & {R\left( 3^{\prime} \right)} & {R\left( 4^{\prime} \right)} \\1 & 1 & 1 & 1\end{matrix}$ of $\begin{matrix}{B\left( 1^{\prime} \right)} & {B\left( 2^{\prime} \right)} & {B\left( 3^{\prime} \right)} & {B\left( 4^{\prime} \right)} \\{G\left( 1^{\prime} \right)} & {G\left( 2^{\prime} \right)} & {G\left( 3^{\prime} \right)} & {G\left( 4^{\prime} \right)} \\{R\left( 1^{\prime} \right)} & {R\left( 2^{\prime} \right)} & {R\left( 3^{\prime} \right)} & {R\left( 4^{\prime} \right)} \\1 & 1 & 1 & 1\end{matrix}^{1}$to obtain

$\begin{matrix}{\begin{pmatrix}{{aYB}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aYG}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aYR}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aY}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} \\{{aMB}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aMG}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aMR}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aM}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} \\{{aCB}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aCG}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aCR}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aC}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} \\{{aKB}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aKG}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aKR}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)} & {{aK}\left( {3^{\prime}\mspace{11mu} 4^{\prime}} \right)}\end{pmatrix} = {\begin{pmatrix}{Y(1)} & {Y(2)} & {Y(3)} & {Y(4)} \\{M(1)} & {M(2)} & {M(3)} & {M(4)} \\{C(1)} & {C(2)} & {C(3)} & {C(4)} \\{K(1)} & {K(2)} & {K(3)} & {K(4)}\end{pmatrix}\begin{pmatrix}{B\left( 1^{\prime} \right)} & {B\left( 2^{\prime} \right)} & {B\left( 3^{\prime} \right)} & {B\left( 4^{\prime} \right)} \\{G\left( 1^{\prime} \right)} & {G\left( 2^{\prime} \right)} & {G\left( 3^{\prime} \right)} & {G\left( 4^{\prime} \right)} \\{R\left( 1^{\prime} \right)} & {R\left( 2^{\prime} \right)} & {R\left( 3^{\prime} \right)} & {R\left( 4^{\prime} \right)} \\1 & 1 & 1 & 1\end{pmatrix}}} & (57)\end{matrix}$As a result, it is possible to calculate the linear masking coefficientaPS (hues 3′ to 4′) (P=Y, M, C, K; S=R, G, B) of the hue areas 3′ and4′. Similarly, it is possible to calculate the linear maskingcoefficient aPS (each hue) (P=Y, M, C, K; S=R, G, B) for other hues.

An embodiment corresponding to a second aspect of the present inventionis explained. It is possible to improve color reproducibility of a copyby changing a printer vector P(i)(P=Y, M, C, K; i=each hue) of Equation57 according to an original type of an original to be copied. Theoriginal type includes a print original for which ink is used as a colormaterial, a printing paper photograph original using a YMCphotosensitive layer as a color material, a copy original using toner asa color material, an ink jet original using an ink jet printer output asan original, a map original using special ink, and a color correctionfor a highlight pen identifying the highlight.

As the printer vector P(i)(P=Y, M, C, K; i=each hue) of the Equation 57,an aPS original type (hue) (P=Y, M, C, K; S=R,G,B, constant)corresponding to each image quality mode is calculated in associationwith each image quality mode selected by an operation section based on acorresponding P original type (i)(P=Y,M,C,K; i=each hue, originaltype=printing, printing paper photograph, copied original, map, ink jet,highlight pen for example). The aPS original type is set in a circuit(ASIC) and used at the time of copying.

$\begin{matrix}{\begin{pmatrix}{{aYB}\mspace{14mu}{Original}{\;\mspace{11mu}}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} & {{aYG}\mspace{14mu}{Original}{\;\mspace{11mu}}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} & {{aYR}\mspace{14mu}{Original}{\;\mspace{11mu}}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} & {{aY}\mspace{14mu}{Original}{\;\mspace{11mu}}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} \\{{aMB}\mspace{14mu}{Original}\mspace{14mu}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} & {{aMG}\mspace{14mu}{Original}{\;\mspace{11mu}}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} & {{aMR}\mspace{14mu}{Original}{\;\mspace{11mu}}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} & {{aM}\mspace{14mu}{Original}{\;\mspace{11mu}}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} \\{{aCB}\mspace{14mu}{Original}\mspace{14mu}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} & {{aCG}\mspace{14mu}{Original}{\;\mspace{11mu}}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} & {{aCR}\mspace{14mu}{Original}{\;\mspace{11mu}}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} & {{aC}\mspace{14mu}{Original}{\;\mspace{11mu}}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} \\{{aCB}\mspace{14mu}{Original}\mspace{14mu}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} & {{aCG}\mspace{14mu}{Original}{\;\mspace{11mu}}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} & {{aCR}\mspace{14mu}{Original}{\;\mspace{11mu}}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}} & {{aC}\mspace{14mu}{Original}{\;\mspace{11mu}}{{type}\left( {3^{\prime} - 4^{\prime}} \right)}}\end{pmatrix} = {\begin{pmatrix}{Y\mspace{14mu}{Original}{\mspace{11mu}\;}{{type}(1)}} & {Y\mspace{14mu}{Original}\mspace{14mu}{{type}(2)}} & {Y\mspace{14mu}{Original}\mspace{14mu}{{type}(3)}} & {Y\mspace{14mu}{Original}{\mspace{11mu}\;}{{type}(4)}} \\{M\mspace{14mu}{Original}\mspace{14mu}{{type}(1)}} & {M\mspace{14mu}{Original}\mspace{14mu}{{type}(2)}} & {M\mspace{14mu}{Original}\mspace{14mu}{{type}(3)}} & {M\mspace{14mu}{Original}{\mspace{11mu}\;}{{type}(4)}} \\{C\mspace{14mu}{Original}\mspace{14mu}{{type}(1)}} & {C\mspace{14mu}{Original}\mspace{14mu}{{type}(2)}} & {C\mspace{14mu}{Original}\mspace{14mu}{{type}(3)}} & {C\mspace{14mu}{Original}{\mspace{11mu}\;}{{type}(4)}} \\{K\mspace{14mu}{Original}\mspace{14mu}{{type}(1)}} & {K\mspace{14mu}{Original}\mspace{14mu}{{type}(2)}} & {K\mspace{14mu}{Original}\mspace{14mu}{{type}(3)}} & {K\mspace{14mu}{Original}{\mspace{11mu}\;}{{type}(4)}}\end{pmatrix}\begin{pmatrix}{B\left( 1^{\prime} \right)} & {B\left( 2^{\prime} \right)} & {B\left( 3^{\prime} \right)} & {B\left( 4^{\prime} \right)} \\{G\left( 1^{\prime} \right)} & {G\left( 2^{\prime} \right)} & {G\left( 3^{\prime} \right)} & {G\left( 4^{\prime} \right)} \\{R\left( 1^{\prime} \right)} & {R\left( 2^{\prime} \right)} & {R\left( 3^{\prime} \right)} & {R\left( 4^{\prime} \right)} \\1 & 1 & 1 & 1\end{pmatrix}^{- 1}}} & (58)\end{matrix}$

A method of calculating hue area determination reference parameter Fx′and a masking coefficient by reading the scanner data calibration chartshown in FIG. 26 is explained with reference to a flowchart of FIG. 57.FIG. 57 is a flowchart of correction by scanner data calibration of thepresent invention.

A scanner data calibration chart is read (S1001). For example, a scannerdata calibration standard chart shown in FIG. 26 is placed on theoriginal stand of the scanner 300 and read by the scanner 300.

A hue angle is calculated (S1002). Based on respective patch read valuesRGB data (Dr, Dg, Db)(=Ri, Gi, Bi (i=each patch number)) of the scannerdata calibration chart, using Equations 13 to 29, parameters GR, GB, andFx′ for dividing RGB image data of read original for each tint arecalculated.

A linear masking coefficient is calculated (S1003). Based on Equation 57and read values Ri, Gi, Bi (i=each patch number) of respective patches,a linear masking coefficient for each hue is calculated.

The read value and the coefficient are stored (S1004).

The color conversion UCR processing circuit 1406 performs thecalculation using the following Equation to perform a color correctionprocessing.Y′=Y−α*min(Y,M,C)M′=M−α*min(Y,M,C)C′=C−α*min(Y,M,C)Bk=α*min(Y,M,C)In the Equation, α is a coefficient for determining an amount of UCR.100% UCR processing is performed when α=1. A value of α may be a fixedvalue. For example, it is possible make an image in a highlight partsmooth by setting α close to 1 in a high concentration part and settingα close to 0 in a highlight part (a low image concentration part).

The masking coefficients are different for each of fourteen huesconsisting of twelve hues obtained by further evenly-dividing six huesof R, G, B, Y, M, and C, respectively, and black and white.

A hue determination circuit 1424 judges in which hue read image data isdistinguished. Based on a result of the judgment, a color correctioncoefficient for each hue is selected.

The enlargement/reduction circuit 1407 performs vertical and horizontalenlargement/reduction. The image processing (create) circuit 1408performs repeat processing or the like. The printer γ circuit 1409corrects an image signal according to an image quality mode (e.g., acharacter, a photograph). The printer γ circuit 1409 can performbackground skip or the like simultaneously. The printer γ correctioncircuit 1409 has a plurality of (ten as an example) gradation conversiontables that can be switched according to an area signal generated by thearea processing circuit 1402. According to the gradation conversiontables, a gradation conversion table optimal for each original (e.g., acharacter, silver salt photograph (printing paper), a print original,ink jet, a highlight pen, a map, or a thermal transfer original) can beselected out of a plurality of image processing parameters. Thegradation processing circuit 1410 performs dither processing. In thedither processing, it is possible to select dither processing of anarbitrary size ranging from 1×1 no-dithering processing to ditherprocessing by m×n pixels (m and n are positive integers). It is possibleto perform the dither processing using up to thirty-six pixels (anexample). A size of a dither using all the thirty-six pixels includes 6pixels in the main scanning direction×6 pixels in the sub-scanningdirection (total thirty-six pixels) or 18 pixels in the main scanningdirection×2 pixels in the sub-scanning direction (total thirty-sixpixels).

Note that the dither processing in gradation processing circuit 1410 isthe same as that in the gradation processing circuit 714 explained inthe first embodiment. Thus, the dither processing is not furtherexplained.

The interface I/F selector 1411 has a switching function for outputtingimage data read by the scanner section 300 for processing by an externalimage processing apparatus or the like or outputting the image data fromthe external host computer or image processing apparatus with theprinter engine 724.

The image formation printer γ (process control γ) correction circuit1412 converts an image signal from the interface 11411 according to agradation conversion table to output a result of the conversion to alaser modulation circuit (described later). The image formation printerγ (process control γ) correction circuit 1412 is referred to as a secondgradation processing circuit below.

The printer section includes the interface 1411, the image formationprinter γ 1412, the printer engine 724, and the controller 1417. It isalso possible to use a scanner and an IPU independently from each other.An image signal from a host computer is input to the interface 1411 viaa printer controller and is subjected to gradation conversion by theimage formation printer γ correction circuit 1412. Since image formingis performed by the printer engine 724, it is possible to use theprinter section as a printer.

The image processing circuit as described above is controlled by the CPU1415. The CPU 1415 is connected to the ROM 1414 and the RAM 1416 via theBUS 1418. The CPU 1415 is also connected to the system controller 1417via the serial I/F such that a command from a not-shown operationsection or the like is transmitted via the system controller 1417. Basedon a transmitted image quality mode, concentration information, areainformation, and the like, respective parameters are set in therespective image processing circuits described above.

The pattern generation circuits 1421 and 1422 generate gradationpatterns used in the image processing section and the image formationsection, respectively.

FIG. 58 is a diagram of a concept of area processing of the presentinvention. In FIG. 58, designated area information on an original iscompared with reading position information at the time of image reading.An area signal is generated from the image separation circuit 1404.Based on the area signal, parameters used in the scanner gammaconversion circuit 1402, the MTF filter circuit 1405, the colorconversion UCR circuit 1406, the image processing 1408, the imageprocessing printer 7 correction circuit 1409, and the gradationprocessing circuit 1410 are changed. In FIG. 58, in particular, theimage processing printer 7 correction circuit 1409 and the gradationprocessing circuit 1410 are shown.

In the image processing printer 7 correction circuit 1409, the areasignal from the image separation circuit 1404 is decoded by the decoder1 and the selector 1 selects a table from a plurality of gradationconversion tables such as a character and ink jet. In an example of anoriginal in FIG. 58, a character area 0, a printing paper area 1, and anink jet area 2 are present. In the example, the character gradationconversion table 1 is selected for the character area 0, the printingpaper gradation conversion table 3 is selected for the printing paperarea 1, and the ink jet gradation conversion table 2 is selected for theink jet area 2.

The image signal subjected to the gradation conversion by the imageprocessing printer γ correction circuit 1409 in FIG. 56 switchesgradation processing to be used with the selector 2 based on a signaldecoded again by the decoder 2 in association with an area signal in thegradation processing circuit 1410. As usable gradation processing,processing not using a dither, processing using a dither, errordiffusion processing, and the like are performed. The error diffusionprocessing is applied to an ink jet original.

For the image signal after the gradation processing, a line 1 or a line2 is selected by the decoder 3. The line 1 or the line 2 is switched foreach different pixel in the sub-scanning direction. Data of the line 1is temporarily stored in a First In First Out (FIFO) memory positioneddownstream the selector 3 and the data of the line 1 and the line 2 isoutput. Consequently, it is possible to reduce a pixel frequency to ½and input the image signal to the I/F selector 1411.

Note that the scanner calibration execution procedure and the like aredescribed in the first embodiment with reference to FIGS. 27 to 55.Thus, explanations of the execution procedure and the like are omitted.

According to the embodiments described above, it is possible to reducedifference appearing in images output by different units of apparatuses.

According to the embodiments described above, it is possible to reducefluctuation in color reproducibility related to a type of an originaldocument in each machine.

According to the embodiments described above, it is possible to use anoriginal read value.

According to the embodiments described above, even when concentrationsor colors in a calibration reference chart fluctuate in the market, itis possible to accurately correct the fluctuation.

According to the embodiments described above, it is possible to improvecolor reproducibility.

According to the embodiments described above, it is possible to reduce adifference of color reproducibility and gradation reproducibility amongmachines.

According to the embodiments described above, it is possible to, when achart other than the calibration reference chart is read by mistake,prevent correction from being executed.

According to the embodiments described above, it is possible to preventdecline in the color reproducibility due to an excessive correctionamount.

According to the embodiments described above, it is possible to select areference value according to a cause of fluctuation in differences amongscanners.

According to the embodiments described above, it is possible to select apresent value according to a cause of fluctuation in differences amongscanners.

According to the embodiments described above, it is possible to reducean influence by flare light.

According to the embodiments described above, it is possible to obtainan accurate read value of an image reading unit.

According to the embodiments described above, it is possible to make iteasy to use ACC pattern reading control software to create anapplication program.

According to the embodiments described above, there is an effect that,it is possible to perform accurate calibration for an image readingunit.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

1. An image forming apparatus, comprising: a color correcting unitincluding a scanning unit configured to optically scan an originaldocument to read an image, and to output an image signal; a firstconverting unit configured to perform a gradation conversion on theimage signal; a hue-area detecting unit configured to detect, among aplurality of hue areas having a plane provided in parallel with abrightness axis in a color space as a boundary, a hue area including asignal color represented by a color image signal; and a correction unitconfigured to correct the signal color according to the hue area; areference-data storing unit configured to store reference datacorresponding to a patch in a reference chart including a plurality ofachromatic patches having different gradation levels and a plurality ofdifferent chromatic patches, the reference chart obtained by reading animage by the scanning unit; and a parameter generating unit configuredto generate, based on the reference data, a hue division parameter to beset in the hue-area detecting unit and a color correction parameter tobe set in the correction unit.
 2. The image forming apparatus accordingto claim 1, wherein the hue division parameter and the color correctionparameter are determined depending on a type of the original document.3. The image forming apparatus according to claim 1, further comprising:a reference-value storing unit configured to store a present valueobtained by reading the reference chart and a previous value beforereading the reference chart; and a previous-value reading unitconfigured to read out the previous value from the reference-valuestoring unit.
 4. An image forming apparatus, comprising: means foroptically scanning an original document to read an image, and to outputan image signal; means for performing a gradation conversion on theimage signal; means for detecting, among a plurality of hue areas havinga plane provided in parallel with a brightness axis in a color space asa boundary, a hue area including a signal color represented by a colorimage signal; means for correcting the signal color according to the huearea; means for storing reference data corresponding to a patch in areference chart including a plurality of achromatic patches havingdifferent gradation levels and a plurality of different chromaticpatches, the reference chart obtained by reading an image by means forscanning; and means for generating, based on the reference data, a huedivision parameter to be used in means for detecting the hue-area and acolor correction parameter to be used in means for correcting the signalcolor.
 5. An image forming apparatus that has a function of outputtingan image read by the image forming apparatus from another image formingapparatus, the image forming apparatus comprising: a reading unitconfigured to read an image, and to output an image signal; a convertingunit configured to perform a gradation conversion on the image signal; achart reading unit configured read a calibration reference chart thatincludes a plurality of chromatic patches having different hue areasthat have a plane provided in parallel with a brightness axis in a colorspace as a boundary, and a plurality of achromatic patches havingdifferent concentrations; a reference-value storing unit configuredstore a reference value corresponding to each of the chromatic patches;a first correcting unit configured to correct R, G, and B signalscorresponding to each of the hue areas based on the reference value anda read value of the chromatic patches obtained by reading thecalibration reference chart; a masking-coefficient calculating unitconfigured to calculate a masking coefficient corresponding to each ofthe hue areas from corrected R, G, and B signals and C, M, Y, and Ksignals corresponding to each of the hue areas; and a second correctingunit configured to correct the image signal on which the gradationconversion has been performed, based on the masking coefficient.
 6. Theimage forming apparatus according to claim 5, wherein the image formingapparatus is configured to convert the read value of the chromatic patchusing a scanner gamma conversion table for correcting a difference inperformance of the reading unit among the image forming apparatuses. 7.The image forming apparatus according to claim 5, wherein the imageforming apparatus is configured to create the scanner gamma conversiontable based on the read value of the achromatic patch.
 8. The imageforming apparatus according to claim 5, wherein the image formingapparatus is configured control, when the read value of the chromaticpatch is out of a predetermined range with respect to the referencevalue in the reference-value storing unit, the first correcting unit andthe masking-coefficient calculating unit not to perform correction basedon the read value of the chromatic patch and calculation based on theread value of the chromatic patch respectively.
 9. The image formingapparatus according to claim 5, further comprising: acorrection-coefficient setting unit configured to set a correctioncoefficient to determine an amount of correction performed on the R, G,and B signals by the first correcting unit.
 10. The image formingapparatus according to claim 5, wherein the reference value is any oneof a design value and the read value of the chromatic patch read inadvance, and the image forming apparatus further comprises areference-value selecting unit configured to select one of the designvalue and the read value.
 11. The image forming apparatus according toclaim 5, wherein the present value is replaceable with a factory-settingvalue that is a standard read value of the calibration reference chart,and the image forming apparatus further comprises a present-valueselecting unit configured to select either one of the factory-settingvalue and the read value that has been read in advance.
 12. An imageforming apparatus that has a function of outputting an image read by theimage forming apparatus from another image forming apparatus, the imageforming apparatus comprising: means for reading an image to output animage signal; means for performing gradation conversion on the imagesignal; means for reading a calibration reference chart that includes aplurality of chromatic patches having different hue areas that have aplane provided in parallel with a brightness axis in a color space as aboundary, and a plurality of achromatic patches having differentconcentrations; means for storing a reference value corresponding toeach of the chromatic patches; means for correcting R, G, and B signalscorresponding to each of the hue areas based on the reference value anda read value of the chromatic patches obtained by reading thecalibration reference chart; means for calculating a masking coefficientcorresponding to each of the hue areas from corrected R, G, and Bsignals and C, M, Y, and K signals corresponding to each of the hueareas; and means for correcting the image signal on which the gradationconversion has been performed, based on the masking coefficient.
 13. Animage forming method, comprising: optically scanning an originaldocument to read an image; outputting an image signal; performing agradation conversion on the image signal; detecting, among a pluralityof hue areas having a plane provided in parallel with a brightness axisin a color space as a boundary, a hue area including a signal colorrepresented by a color image signal; and correcting the signal coloraccording to the hue area; storing reference data corresponding to apatch in a reference chart including a plurality of achromatic patcheshaving different gradation levels and a plurality of different chromaticpatches, the reference chart obtained by reading an image; andgenerating, based on the reference data, a hue division parameter to beused at detecting the hue-area and a color correction parameter to beused at correcting the signal color.
 14. An image forming method forforming an image in an image forming apparatus that has a function ofoutputting an image read by the image forming apparatus from anotherimage forming apparatus, the method comprising: reading an image;outputting an image signal; reading a calibration reference chart thatincludes a plurality of chromatic patches having different hue areasthat have a plane provided in parallel with a brightness axis in a colorspace as a boundary, and a plurality of achromatic patches havingdifferent concentrations; storing a reference value corresponding toeach of the chromatic patches; correcting R, G, and B signalscorresponding to each of the hue areas, based on the reference value anda read value of the chromatic patches obtained by reading thecalibration reference chart; calculating a masking coefficientcorresponding to each of the hue areas from corrected R, G, and Bsignals and C, M, Y, and K signals corresponding to each of the hueareas; and correcting the image signal on which the gradation conversionhas been performed, based on the masking coefficient.